THE SMITH-KETTLEWELL TECHNICAL FILE

A Quarterly Publication in Braille Talking Book and IBM Diskette Editions from The Rehabilitation Engineering Center The Smith-Kettlewell Eye Research Institute

Bill Gerrey, Editor

Supported, in part, by The Smith-Kettlewell Eye Research Institute and National Institute on Disability and Rehabilitation Research

Braille Edition Produced by Clovernook Printing House Cincinnati, Ohio

Talking Book and IBM Diskette Editions Produced by The Smith-Kettlewell Eye Research Institute San Francisco, California

1994-95 SUBSCRIPTIONS

Braille Edition . . . . . . . . $18 per year

Talking Book Edition . . . . . $14 per year

IBM 5-1/4" Diskette Edition . . $16 per year

Make checks payable to:

The Smith-Kettlewell Eye Research Institute
2318 Fillmore Street
San Francisco, California 94115

Please address all correspondence to: Bill Gerrey, Editor at the above address or call: (415) 561-1619

E-mail: rerc@.ski.org

World Wide Web: http://www.ski.org/rehab/

VOLUME 14, NO. 3 (1994-95)

TABLE OF CONTENTS

A Simple Appliance Timer Using Two Talking Alarm Clocks

Evaluating the Cobolt "Speech Master" Timestat as an Appliance Timer

A Rejuvenator/Evaluator for Talking Book Batteries

A SIMPLE APPLIANCE TIMER USING TWO TALKING ALARM CLOCKS

Abstract

Blind tape-recording enthusiasts and users of other home appliances have long awaited an accurate device for turning equipment on and off at predetermined times. Since talking clocks have become so readily available, it was reasoned that many of us have a couple to spare, and if not, prices are low enough so that two clocks and this sound-triggered relay circuit could cost under $100. The alarm sound from one clock turns the power on, and the alarm of the second clock turns the power off. No modification to the clocks is necessary; audio to operate the system is captured by inductive pickup. This does mean, however, that the clocks used must have magnetic loudspeakers, as most do.

Introduction

We have all been hoping that appliance manufacturers would either make products "talk" their display information, or that they might at least make it convenient to attach talking or Braille readout devices to them. Nope, neither accommodation has come about.

The next elegant solution was a pending product, a special talking appliance timer. Indeed, Mr. and Mrs. Fowle designed this instrument -- very fancy, too, with the capability of turning various things on and off at different times. However, as with all special products of any sophistication, it is difficult to affect "technology transfer" (bringing a device through production to our small market at reasonable cost).

Oh, for the good-ol' days of mechanical clocks which did this very thing. Remember the "James Remindo Timer" and the G.E. "Telechron Clock"? These had levers every fifteen minutes around the face; you pulled as many as you wanted to set the "on" time. Ever since the invention of the wire recorder, my father used those clocks to capture his radio programs day and night. I've got a drawer full of them, all with worn-out irreplaceable motors.

Well, when I lose patience, I'll come up with a silly solution, and let the microprocessor take the hindmost. I will admit that this design is clumsy, but I had its principle working in one afternoon. The clumsiness comes from the fact that, on certain models of clocks, a rubber band holding the pickup coil in place makes it hard to set the alarm.

Description

The system has three components: two are commercially available talking alarm clocks (one to turn the appliance on and the other to turn it off), with the third component being a sound-actuated relay circuit that responds to audio from the clocks. Since many such clocks are small travel models, and thus difficult to modify, direct connection to the clocks' audio system was not deemed appropriate.

It was decided that inductive pickup from the loudspeakers of the clocks would be best. Acoustic microphones would trigger the system as well, but this would be vulnerable to any loud sound source.

Telephone inductive pickups are inexpensive and readily available from Radio Shack. The typical configuration is a round plastic capsule containing a coil on an iron core, this assembly being fitted with a rubber suction cup for attachment to the earpiece of the phone. A standard "mini phone plug" allows connection to microphone inputs of tape recorders or other amplifying devices.

The major disadvantage of using inductive pickup is that positioning each pickup coil over the loudspeaker of its talking clock is very critical. The coil picks up incidental flux leakage from the magnetic circuit of the speaker, and this field is only of sufficient intensity when the pickup is exactly centered over the voice coil of the speaker.

Induction has another vulnerability too: a nearby computer monitor, as well as motors and power transformers in nearby equipment, might be detected by the circuit. So that the coils can be precisely positioned, and to afford monitoring of interference when it occurs, an amplifier and speaker is included in the sound-activated relay device.

Setting up the system requires scanning the speaker grille of each clock with its pickup coil while making the clock speak, thus determining the position of highest output. While the coils used have suction cups for attachment to telephone earpieces, these cannot adhere to a porous speaker grille; wide rubber bands are best for holding the coils to their respective clocks. Once the loudest position of each coil is found, careful listening is required so that the clocks can be placed where "hum" and other external electromagnetic noise is minimized.

At this point, the system should be tested to see if speech from the clocks is of sufficient level to trip the relay. With the volume on the device turned down, you will be able to hear the mechanical "clicking" of the relay as the clocks are made to trip and release it. Or, an appliance plugged into the relay can, by its activation, tell the user if "tripping" of the relay is taking place.

Because the heart of the sound-actuated relay is an RS flip-flop, multiple outbursts from a clock will not "toggle" the relay on and off; in other words, once the first clock causes the relay to close, only a signal from the second clock will open it. This is fortunate, since some clocks sound their alarm more than once. This does mean, though, that if a Sharp "Talking Time I," whose alarm sounds three times over a period of fifteen minutes, is used to turn on an appliance, the earliest time it can be turned off is sixteen minutes after initiation.

Theory of Operation

Signals from the pickup coils are amplified 40dB by op-amps in the LM324; the preamp outputs are pins 1 and 14 of the 324. Outputs of the preamplifiers are combined in the volume control and fed to the LM386 power amplifier and loudspeaker circuit.

The remaining op-amps are used as comparators. Their non-inverting inputs look at a voltage of perhaps 1/2 volt above that of the bias point of the preamps. Their inverting inputs go to the outputs of their respective preamps; as soon as a voltage swing exceeds that of the upper junction on the reference voltage divider, an output goes low, triggering the following flip-flop.

A "NOT-R/NOT-S" flip-flop is made using two NAND gates in the 4011. The remaining two NAND gates are connected in parallel and are used to buffer (as well as invert) the "NOT Q" output of the flip-flop.

The 2N2222 transistor is used as a switch to energize the relay coil. The diode shunting this coil suppresses spikes when the relay is de-energized.

Circuit for the Double-Clock Appliance Timer--A 10-amp extension cord is cut in two. The "line cord" (the piece having the male plug) supplies continuous power to the electronics via a 12-volt center-tapped transformer (such as the Radio Shack 273-1365). The cord with the receptacle is switched by the contacts of a double-pole relay. Power connections are as follows:

The "neutral" side of the receptacle goes to the swinger of one pole on the relay. The neutral lead of the line cord goes to the normally open contact of this relay pole. One side of the transformer primary winding goes to the neutral side of the line cord. (The neutral side is the broad -- wide -- prong of the plug, and the corresponding longer slot in the receptacle.)

The "hot" side of the line cord goes to two fuses, a 10-amp slow-blow and a 1/4-amp slow-blow. The far end of the 1/4-amp fuse goes to the other side of the transformer primary. The far end of the 10-amp fuse goes to the normally open contact of the second pole on the relay. The swinger of this pole goes to the hot side of the receptacle.

The full secondary of the transformer feeds a bridge rectifier, Radio Shack 276-1152. The output of this bridge will be about 18 volts peak. Alternatively, discrete diodes can be used. In the latter case, the ends of the winding go to the cathodes of two 1N4001 diodes; the anodes of these diodes go to the negative supply line and to ground. The transformer secondary leads also go to the anodes of two more 1N4001 diodes; the cathodes of these go to the plus 18V line. This 18V line is bypassed to ground by 2200uF 35V electrolytic (the negative of this cap going to the first diode anodes and to ground).

Pin 4 of an LM324 quad op-amp goes to VCC; Pin 11 is grounded. A 4011 quad NAND gate has its pin 7 grounded; pin 14 goes to VCC. A voltage divider of three resistors is wired as follows. VCC goes through 100K, then through 10K, then through another 100K to ground. Both junctions with the 10K resistor are bypassed by 10uF (negative of these caps at ground).

Two 1/8-inch mini jacks (for telephone pickup coils) have their sleeves grounded. Being of the closed-circuit type, their switch contacts are also grounded.

The tip contact of one jack goes through 0.022uF, then through a 10K resistor to pin 2 of the LM324. Between pins 2 and 1 is the parallel combination of a 1 megohm feedback resistor and a 68pF disc capacitor.

In like manner, the tip contact of the other jack goes through 0.022uF, then through a 10K resistor to pin 13 of the 324. Between pins 13 and 14 is a 1 megohm feedback resistor in parallel with a 68pF disc capacitor.

On the 324, pins 3 and 12 (both non-inverting inputs) go to the lower junction on the voltage divider. Pins 5 and 10 of the 324, non-inverting inputs of the "comparators," go to the upper junction of the divider.

Pin 6, the inverting input of a comparator, goes to pin 1, the output of its preamp. Likewise, pin 9 goes to pin 14.

Pins 2 and 4 of an LM386 audio amplifier are grounded; pin 6 goes through a 47-ohm 1/2-watt resistor to the center tap of the transformer secondary; pin 6 is bypassed to ground by 220uF (a 16-V electrolytic with its negative end at ground). Pin 7 of the 386 is bypassed to ground by 10uF (negative of this cap at ground).

Pins 2 and 3, inverting and non-inverting inputs, are shunted by 0.01uF. Pin 3 also goes through 0.1uF to the arm of a 10K volume control; the bottom of this pot is grounded. Each preamp output, pin 1 and pin 14 of the LM324, goes through its own 47K resistor to the top of the volume control.

The output of the 386, pin 5, is bypassed to pin 4 by 0.1uF. Pin 5 also goes to the positive end of a 100uF cap, with the negative end going through a loudspeaker to ground.

Two gates in the 4011 quad NAND chip are wired as an RS flip-flop. Pin 10, an output, goes to pin 12, the input of another gate. Pin 11, the output of this second gate, goes to pin 9, an input of the first gate.

The "NOT set" (pin 13 of the 4011) goes to pin 8 of the LM324, the output of a comparator. The "NOT reset" (pin 8 of the 4011) goes to pin 7 of the 324, the other comparator output.

The two remaining gates in the 4011 are connected in parallel so as to act as a buffer. Their outputs, pins 3 and 4, are tied together. Input pins 1, 2, 5 and 6 are tied together and go to pin 10 on the same chip (pin 10 being the "NOT Q" output of the flip-flop).

Pins 3 and 4 of the 4011 also go through 2.2K to the base of a 2N2222. The emitter of this transistor is grounded. Its collector goes through the coil of a relay to VCC. The coil of the relay is shunted by a diode, a 1N4003, with the cathode of this diode at VCC.

Parts List

Resistors (1/4-watt, 5% unless otherwise specified):

Capacitors:

Semiconductors:

Miscellaneous:

Suitable Clocks:

Radio Shack sells a 12-volt DPDT relay with 10-amp contacts, Cat. No. 275-218. (Its optional matching socket is No. 275-220. The author found it easy enough to solder directly to the prongs of the relay.)

A good power transformer is one with magnetic shielding, such as the Radio Shack 273-1365 (12.6V 400mA.). The bridge rectifier used is Radio Shack 276-1152 (1.4-amp 100 PIV).

The telephone pickup coils are Radio Shack 44-533, and are found in the section of tape recorder accessories.

The clocks used must have an electromagnetic speaker, so that "inductive pickup" is possible. Most do, but others, even within the same brand name, do not. (A significant number use piezo-electric speakers, which are less heavy and very low-profile.)

Originally, the author intended to list suitable model numbers. However, a multitude of brands are scattered throughout suppliers of products for the disabled and blind, and the task seemed endless. (Plus, mail-order dealers have no way of finding out which ones won't work.)

You find out which clocks are good by repeatedly actuating them while searching around their speaker areas with one of the pickup coils; an amplified sound of the time announcement will be heard from the loudspeaker in this relay device.

EVALUATING THE COBOLT "SPEECH MASTER" TIMESTAT AS AN APPLIANCE TIMER

Abstract

An inexpensive commercial product, the "Timestat" made by Cobolt, in England, is a ready-made appliance switch that can be set to turn appliances on and off on the basis of time and/or temperature. Purported as a controller of electric heaters (to keep persons from accidentally freezing to death), it is of interest to those of us who wish to control our tape recorders, electric cooking appliances, etc. Limited to a 10-amp switching current, it is not suitable for controlling electric heaters in countries where 117 volts is the standard for the mains.

[Editor's Note: Just about the time that I was overcome by my cleverness -- designing the "Talking-Clock-Driven Appliance Timer" (see previous article), Vito Proscia of IRTI, (415) 961-3161, let me know of this product. I dropped my soldering iron, had a big lunch, and declared, "Well that problem's solved." Not quite, but if you can afford the modest $135, it is worth having one of these around.]

Description

The Timestat comes in a very attractive Bakelite cabinet: 7-3/4 by 4-3/8 by 2-3/8 inches. (The fact that the cabinet is unshielded Bakelite is of considerable impact in the author's evaluation.) Protruding from the rear are three items: a heavy cable for plugging into the mains, a heavy 8-inch cable bearing a socket for a single appliance, and a temperature sensor. (The temperature sensor, mounted in a stalk of heat-shrinkable tubing, protrudes about one inch.)

Besides having a manual on/off feature and two separate timers (which can each be set to turn on for specified days of the week), the device can turn on something below a set temperature. Finally, it has a "frost-stat" mode, wherein it will turn on at the freezing point of water, regardless of other settings.

A point of note here is what the unit is designed for. The topic of discussion in the instruction sheet is controlling an electric heater. The switching device is a small relay whose contacts are rated at 10 amps. In England, where it comes from, mains of 220 volts are common; a 10-amp heater can be imagined. Here in the U.S., 117 volts is standard. Presumably, the power transformer in the U.S. model running the electronics is also chosen for the American standard (especially with the style of plugs they send the Timestat with). Here, we don't have 10-amp heaters -- the closest is 1200 watts (10.25 amps, with a predictable surge current of much more than this). Many of our 117-volt heaters are 13-amp (1500-watt).

On the top are eight square buttons; the bottom three of these are turned at 45 degrees, apparently attempting to make them more identifiable by touch.

Immediately upon plugging in the device, a sketchy description of its operation is given (following a time and date announcement): "Buttons on the top row select functions. Buttons on the center row give time, timer, and temperature, and select set modes. Buttons on the bottom row give day, adjust volume, and adjust settings. Generally, press buttons once for current settings; press again, within two seconds, to alter." (It says these sentences in a most beautiful recorded voice.)

Impressions

The eight square buttons are arranged with two in the top row, three in the middle row, and three (turned 45 degrees) along the bottom. Not providing a 16-button touchpad with which we are all familiar, eight buttons means that the operator must navigate in a menu system, a system the machine patiently talks you through. This author, however, constantly gets lost in the menu system. For example, I must try and try again to set the "day" of a particular "on" time.

Setting the clock is no friendly process; repeated pressing of hour and minute buttons is required. Holding a button down does not cause the device to step rapidly through hours and minutes. Furthermore, pressing them in rapid succession makes little progress; you can easily "outrun" the machine by pressing more often than about four times per second. Thus, it is the author's opinion that a touchpad entry system would be superior.

If you wish to check a setting, you must listen to the announcement of settings for both timers. If you have the timers set for certain days of the week, this can be a long speech; no provision to shut the thing up is provided.

My Timestat runs fast -- by a few minutes in half a year. Thus, when I have to reset the clock, I must cycle through 23 hours and fifty-some minutes -- a great inconvenience. (Holding a button down does not cause rapid stepping through a sequence; you must press the button for every step.)

They have used lovely buttons -- large and easy to feel. In choosing this arrangement, they have selected a simple control panel to perform too many operations.

Bill Gerrey's Evaluation

The unit seems sturdily built, although the speaker and temperature sensor are anchored with "hot glue," which is not a chemical bond as would be true of cement. The digitized speech recording is gorgeous, the best I've heard in a self-contained talking product.

There is an oddity about the timer settings: I cannot seem to get the clock and timer settings closer than within 20 seconds of when I want them. It's as if there is a limit to resolution of the selection. Not a big point, but many of us have been spoiled by the split-second precision of our talking alarm clocks.

The Timestat would be a nice indoor thermometer if it were more accurate. The author's reads consistently higher than other thermometers that I trust -- higher by at least 5 degrees Fahrenheit. Once again, its design speaks of life-saving intent, not utility for those of us who want utility above necessity. Readings of the thermometer may best be interpreted loosely. (Were you to have the 220-volt version and a heater to match, this device would be reliable enough to keep you out of danger in your sleep.)

There is a frailty of the physical design that is quite bothersome -- radio interference from the Timestat. It has a 16MHz crystal and, man oh man, shortwave, and even FM broadcast receivers are tortured by carriers generated by stuff in the Timestat's unshielded box. Luckily, a nickel cadmium battery preserves settings and keeps the clock running when it is unplugged, because disconnected is how you will want it much of the time.

All-in-all, the price is right, and I'm glad I have one.

Availability

I haven't checked all the suppliers. I know that Vito at IRTI sells them; phone: (415) 961-3161.

A REJUVENATOR/EVALUATOR FOR TALKING-BOOK BATTERIES

APH Catalogue No. 1-7070-0, Panasonic P-12-6U01

Abstract

A troublesome component of cassette players issued by the Library of Congress for the "Talking Book Program" is the nickel cadmium battery pack. From time to time, we have been asked by state services to build a device with which batteries of returned machines may be quickly checked. For example, can a battery be brought up to its full terminal voltage, and if so, will it hold a charge? If there is a shorted cell in the pack, can the short be cleared? This is the latest of our designs of such an instrument. Quick charge and discharge characteristics can be "observed," and an attempt to "clear" shorts in the string of cells can be made.

(Note: Early versions of these packs bore a series of G.E. numbers much different from the APH catalogue number listed here. My very earliest, circa 1973, could be taken apart; it was made with two telescoping halves. If you ever get your hands on one of those, save it, since you can put a voltage regulator in the case to run off any sort of supply--a car cigarette lighter, for example.)

Introduction

The battery pack--APH No 1-7070 (on its label bearing a Panasonic No. P-12-6U01)--is rated as having a 1.2 amp-hour capacity. It contains 6 "sub-C" cells; its terminal voltage is typically 7.2 to 7.5 volts. To make optimum use of it, it should be charged at 120mA for 14 to 16 hours, then left to run its device until its voltage drops below 6 volts or so, then charged again.

Unfortunately, the cassette machines using these batteries are often left plugged in, thus charging their battery until chemical reactions within the cells damage the capacity. Furthermore, infrequent use of a machine on battery power causes a sort of "memory effect" which reduces battery capacity. Worst of all is when stronger cells in the string last long enough to "reverse charge" weaker ones; shorted cells in the series will be the result. Finally, batteries left on the shelf often develop shorted cells.

In testing and salvaging these batteries, it makes sense to perform the following operations:

When charging, does the battery reach a level comparable to its terminal voltage (usually about 20% higher than that on cells which are not leaky) ?

When discharged at the same rate as the charging current, is the time taken to drop below an unacceptable voltage somewhere between one-half to two-thirds of the charging time?

If the rated voltage cannot be reached, does a mild high-current shock to the battery clear shorts in cells so as to restore them back to life?

These are features we designed into the test set described below:

Description

Our unit was built into a cabinet of 4-1/4 by 7-1/2 inches, and whose depth is 2-3/8 inches. A battery holder on the top of the box consists of two wooden blocks; one has a recessed contact in which a 0.300-inch hole can only accept the small battery terminal (the positive); the other block holds a springy piece of shim stock that contacts the larger battery terminal (negative).

Also on the top panel are the following controls:

1. A 3-position rotary switch selects: (1) a normal discharge load of 10% amp-hour capacity, which also allows a test of battery voltage under a light load, (2) a normal charge rate of 120mA (for overnight charging), and (3) a quick-charge/discharge assessment (at approximately 1 amp).

2. Associated with position 3 of the rotary switch listed above, a momentary switch (pushbutton or "momentary toggle") connects the high-current charging circuit; releasing this switch puts the battery under a heavy load of similar current drain.

3. A high-current toggle switch connects a large electrolytic capacitor across the battery with the intention of "burning out" minor shorts within cells of the pack.

4. A small toggle switch allows the audible indicator to be turned off--especially desirable when slowly charging a battery.

The heart of the metering circuit is "The Smith-Kettlewell Auditory Battery Tester," published in Vol. 11, No. 1 of SKTF (Winter 1990). In the range of interest, the instrument emits "tone bursts" whose length increases until the battery is judged to be dead, whereupon the bursts blend together into a steady tone. Put another way, the shorter the "pips" (bursts of the tone), the better the battery. An added feature to the output of this instrument is that the pitch of the tone drops as the battery voltage declines; thus, a good qualitative indication of the discharge rate can be had.

In operation, the user might start with the instrument in the simple battery-test position--with the rotary switch in position 1 and with the audible indicator turned on. (The audible indicator emits a low buzz, in the test position, for either no battery or a dead one, just to let you know it is on.) Placing the battery in the holder, the response of the auditory output is then noted; if the pitch rises and the tone is interrupted to produce "pips," the battery is at least partially charged and all cells are working.

If in the above test, the buzz does not change in pitch, or if it does, but is steady and not interrupted, an attempt must be made to put a charge on the battery. Switching to position 2, the normal charge position, a favorable indication would be to hear the pitch rise and interruptions in the tone begin; this would mean that all the cells are probably unshorted, and that all the battery needs is to be charged.

A well-used battery may seem like it is charging, but it may not hold a charge when put into service. For this test, the rotary switch should be advanced to position 3. With the auditory indicator still left on, hold the momentary switch in the charging position. (The indicator may fall silent while charging in this high-current mode, since the battery voltage may exceed its range of indication.) After some time, perhaps 30 seconds, release the momentary switch and listen to the indicator. In this mode of heavy discharge, the bursts of the indicator tone will grow longer until they blend together, and the pitch will drop. The battery is still usable if it takes longer than 15 seconds for the "pips" to blend together and the pitch descends rapidly. It is best to keep some charge in the battery if it is to be set aside for later use; you may use the quick-charge feature to bring it up to a "good" indication, then quickly remove it from the instrument so as not to discharge it through the load.

If a 30-second quick charge does not bring the battery up to the point where the tone is interrupted, imparting a shock to it is the last opportunity to salvage it. Put the rotary switch in position 2 (normal charge) and flip the high-current toggle switch to connect the capacitor to the battery. (Leaving this toggle switch in either position will not hurt anything.) At this point, note the indicator; treat this as if you have just installed the next battery to be tested. You may shock a battery as many times as you like, but if two or three tries don't make it appear functional, it should be discarded. (It takes several seconds to fully charge the large capacitor, so do not throw this switch back and forth rapidly for multiple shocks to the battery.)

If the battery revives after the high-current shock and passes the aforementioned tests, it is a good idea to put a full 16-hour charge on it, either in this test instrument or in a talking-book machine.

Circuit for the Talking-Book Battery Tester

A 12.6V center-tapped transformer good for at least 1.2 amps is used (such as the Radio Shack No. 273-1352A, or Allied Electronics No. 705-0121). The primary goes to the 117V AC line; one leg of the primary contains a 1/4-amp slow-blow fuse.

The ends of the secondary feed a high-current bridge rectifier (such as the Collmer KBL0A, available from Allied). The negative output of the bridge is grounded. The positive output of the bridge goes to the 16V line; this is bypassed by 220uF (negative of this cap at ground). The centertap of the secondary goes through a 10-ohm 1/2-watt resistor to the 8V line; this is bypassed by 220uF (negative of this cap at ground).

An LM336 2.5V standard has its "anode" grounded; its "cathode" goes through 1.6K to the 8V line. The junction of the 1.6K and the 336 is the 2.5V point. This 2.5V point goes through two 10K 1% resistors in series to ground. The junction of these resistors is bypassed by 1uF (negative of this cap at ground). The junction of these 10K resistors is called the "unbuffered 1.25V point."

An Lm324 quad op-amp has pin 4 going to the 8V line; pin 11 is grounded. Pin 3 of the 324 goes to the aforementioned unbuffered 1.25V point. Pins 1 and 2 are tied together, and this junction goes to the buffered 1.25V line.

Pin 7 of the 324 goes through 47K to the gate of a VMOS power FET (such as a VN0300M, VN10KM or VN10LM). The source of this FET is grounded. The FET drain goes through 1.6K to the 2.5V point. Pin 10 of the 324 goes to the unbuffered 1.25V point. Between pins 8 and 9 is a 0.22uF mylar capacitor. (Since this is a bidirectional integrator, this cap must be nonpolar.) Pin 9 goes through 1.8 megohms to the 2.5V point. Pin 9 also goes through 910K to the collector of a 2N2222 transistor. The emitter of this 2222 is grounded. Its base goes through 47K to the drain of the VMOS FET.

The drain of the FET also goes through 120K to the top of a 50K trim pot. The bottom of this pot goes to pin 1 of the 324, the buffered 1.25V line. The arm of the trim pot goes to pin 6 of the 324. Pin 5 of the 324 goes to its own pin 8.

Pin 8 of the 324 also goes to its own pin 12. Pin 13 goes to the arm of another 50K trim pot. The bottom of this pot goes through 4.7K to ground. The top of this pot goes through 200K to the "hot input" of the audible tester, the cold input being ground.

A 555 timer chip has pin 1 grounded. Pins 4 and 8 are tied together and go through a 10-ohm 10-watt resistor to the 8V line. Between pins 1 and 8 is the parallel combination of 0.1uF and 220uF (negative of the latter at pin 1).

Pins 2 and 6 of the 555 are tied together and go through 0.01uF to ground. Pins 2 and 6 also go through 47K to pin 7. Pin 7 also goes through 1.8 megohms to the 8V line. Also from pin 7 is a 47K resistor in series with a 1N914 diode to the hot input of the tester (the anode of this diode at the input).

Pin 3 of the 555 goes through an 82-ohm 1/2-watt resistor to one side of the loudspeaker. The other side of the speaker goes through an SPST switch to the 8V line. (This switch turns the audible indicator on and off.)

The negative side of the battery's test connector is grounded. The positive side of the battery connector goes to the hot input terminal of the audible tester.

A 2-pole 3-position switch is used for mode selection. (The author used a four-pole unit with pairs of poles connected in parallel to minimize contact resistance.)

On the first pole, the swinger goes through a 68-ohm, 3-watt or higher (Allied Cat. No. 880-0217) resistor to the positive terminal of the battery connector. Position 1 of this pole is grounded, while position 2 goes to the 16V line. Position 3 of this pole is left open.

On the second pole, the swinger goes through a 7.5-ohm 10-watt resistor (Allied Cat. No. 875-1096) to the positive battery terminal. Positions 1 and 2 of this pole are left open. Position 3 goes to the swinger of an SPDT momentary switch. The normally closed position of this latter switch is grounded; the normally open contact goes to the 16V line.

The rejuvenation circuit requires a large capacitance; the author used two 22,000uF caps in parallel (Allied Cat. No. 926-4120). The switch used is a heavy-current SPDT toggle--a so-called "three-way" light switch from a hardware store.

The negative side of the electrolytic goes through 18-gauge wire to the negative of the battery connector, which is also ground. The positive of the electrolytic goes through perhaps a 1/2-ohm 3-watt resistor (Allied No. 880-0204) to the swinger of the switch. The "normal" position of this switch goes through 68 ohms (not critical) to the 16V line. The "shock" position of this switch goes through 18-gauge wire to the positive battery connector.

Parts List

for APH Catalogue No. 1-7070-0, Panasonic P-12-6U01 Battery Tester

Capacitors:

Resistors (1/4-watt, 5% unless otherwise stated):

Potentiometers:

Semiconductors:

Miscellaneous: