Silicon ChipTwin-Cell Nicad Discharger - November 1994 SILICON CHIP
  1. Outer Front Cover
  2. Contents
  3. Publisher's Letter: Tiny electronic components can be hard to see
  4. Feature: Anti-Lock Braking Systems; How They Work by Julian Edgar
  5. Project: Build A Dry-Cell Battery Rejuvenator by Darren Yates
  6. Project: A Novel Alphanumeric Clock by Anthony Nixon
  7. Serviceman's Log: Tread carefully with a new brand name by The TV Serviceman
  8. Project: UHF Radio Alarm Pager by Branco Justic
  9. Project: 80-Metre DSB Amateur Transmitter by Leon Williams VK2DOB
  10. Project: Twin-Cell Nicad Discharger by Darren Yates
  11. Vintage Radio: Resurrecting a pair of old AWA C79 chassis by John Hill
  12. Feature: Computer Bits by Darren Yates
  13. Feature: How to plot patterns directly to PC boards by John Clarke
  14. Feature: Remote Control by Bob Young
  15. Product Showcase
  16. Back Issues
  17. Market Centre
  18. Advertising Index
  19. Outer Back Cover

This is only a preview of the November 1994 issue of Silicon Chip.

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Items relevant to "A Novel Alphanumeric Clock":
  • Novel Alphanumeric Clock PCB pattern (PDF download) (Free)
Items relevant to "80-Metre DSB Amateur Transmitter":
  • 80m DSB amateur transmitter (PDF Download) [06110941] (PCB Pattern, Free)
Items relevant to "Twin-Cell Nicad Discharger":
  • Twin-Cell Nicad Discharger PCB pattern (PDF download) [14305931] (Free)
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  • Computer Bits (July 1989)
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  • CMOS Memory Settings - What To Do When The Battery Goes Flat (May 1995)
  • Computer Bits (July 1995)
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  • Computer Bits: Connecting To The Internet With WIndows 95 (October 1995)
  • Computer Bits (December 1995)
  • Computer Bits (January 1996)
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  • Windows 95: The Hardware That's Required (May 1997)
  • Turning Up Your Hard Disc Drive (June 1997)
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  • Computer Bits: The Ins & Outs Of Sound Cards (August 1997)
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  • Computer Bits (November 1998)
  • Computer Bits (December 1998)
  • Control Your World Using Linux (July 2011)
Articles in this series:
  • Remote Control (August 1994)
  • Remote Control (September 1994)
  • Remote Control (November 1994)
Modifying the Nicad Cell Discharger to discharge 2-cell packs If you’re looking for a twin-cell nicad pack discharger, this simple modification to the Nicad Cell Discharger described in the May 1993 issue will enable you to do the job. to begin discharging the battery pack. At the same time, IC2a compares the battery pack voltage with a reference voltage de­rived from ZD1 via VR1. Provided that the battery voltage is higher than the reference, IC2a’s output (pin 1) remains high and so Q1 remains on and power is applied to IC1 when the START switch is released. When the battery voltage subsequently falls below 2.2V, pin 1 of IC2a switches low and Q1 switches off and removes power to IC1. This in turn switches Q2 off and so the battery pack ceases discharging. IC2b is configured By DARREN YATES Over the last couple of years, we’ve presented a number of nicad dischargers and they’ve all been very popular. The only problem is that we haven’t catered for those people wanting to discharge two-cell (2.4V) nicad packs. Our most recent circuit for a nicad discharger was pub­lished in the September 1994 issue and this catered for battery packs with 3-10 cells. Another circuit published in May 1993 was designed to discharge single cells only, including AAA, AA, C and D types. That circuit contained a number of desirable features, including a flashing LED indicator to indicate discharging and automatic switch-off at 1.1V. Recently, we decided to take a closer look at this circuit to see if it could be converted to discharge a two-cell pack. As it turns out, the modifications are quite simple. Circuit diagram The new circuit is shown in Fig.1. We won’t go into all the details again. Briefly, IC1 is configured as a 1.5V to 9V DC step-up converter and this is used to power comparator stage IC1a and oscillator stage IC1b. When the START switch (S1) is pressed, IC1 starts and turns on Q2 START S1 D1 1N4004 STEP-UP VOLTAGE CONVERTER S D 2x NICAD CELLS 2.7k Q1 MTP3055 +2.4V L1 50uH G R 2 8.2 0.5W C 470 16VW Q2 BC328 B Fig.1: only a few modifications are required to the front end of the original circuit to convert it to a twin-cell discharger: (1) the two 1Ω resistors are deleted; (2) the positive rail from the battery is now connected to D1’s anode; & (3) the 6.8Ω resistor is changed to an 8.2Ω 1W resistor. 4 6 3 2 0.1 8 IC1 TL496 5 +8.8V 7 10k 3 15k VR1 10k ZD1 BZX79 C5V1 8 5 1 IC2a LM358 2 6 10  10 16VW EXTRA DISCHARGE L1: 33T, 0.5mm ECW ON NEOSID 17-732-22 TOROID B E TWIN CELL NICAD DISCHARGER 66  Silicon Chip VIEWED FROM BELOW C A GDS 1.5k 18k COMPARATOR REFERENCE 7 IC2b 10k 4 0.1 E  SEE TABLE 2.2k 10k 680  470 16VW R1 1.5k 6.8k 470k K A LED1 DISCHARGING DISCHARGING FLASHER  K TABLE 1 SATELLITE SUPPLIES Cell Capacity Discharge Current Q2 R1 R2 1800mAh (AAA) 125mA no - - 500mAh (AA) 125mA no - - 1.2Ah (C) 185mA yes 1.5kW - 2Ah (C,D) 185mA yes 1.5kW - Aussat systems from under $850 4Ah (D) 405mA yes 1.5kW 8.2W SATELLITE RECEIVERS FROM .$280 LNB’s Ku FROM ..............................$229 Q1 IC1 TL496 470k 2.2k 0.1 1 0.1 680  D1 S1 1.5k IC2 LM358 10 R2 8.2  TO NICAD CELL HOLDER 1 2.7k 470uF 6.8k L1 10k 10k A 18k ZD1 K 10k 10uF VR1 Q2 470uF R1 1.5k as a Schmitt trigger oscillator and is used to flash LED 1 on and off during the discharge cycle. Note that Q2, R1 and R2 are only used for the larger cells, to increase the nominal discharge rate. These components can be left out of circuit for AAA and AA cell packs. Circuit modifications The modifications are all at the front end of the circuit. First, the two 1Ω resistors used in the reverse polarity protec­tion network have been deleted and the positive rail from the pack is now connected to D1’s anode. Next, the 6.8Ω 0.5W resistor in series with Q2’s collector is changed to an 8.2Ω 1W resistor. And that’s all there is to it. What happens now is that D1 is connected in series with the batteries and drops the voltage applied to IC1 (via Q1) to 1.8V. This is well within the parameters of IC1. As an added bonus, this modification means that no current is consumed by the circuit when the cells are accidentally connected in reverse, whereas before the consumption was almost 1A. Construction The circuit can be built on the same PC board as before (code 14305931) LED1 Fig.2: this revised parts layout diagram includes all the modifications listed in the text. Note that Q2, R1 & R2 can be left out for AAA & AA cells but may be required for larger capacity C & D cells (see table). LNB’s C FROM .................................$330 FEEDHORNS Ku BAND FROM ......$45 FEEDHORNS C.BAND FROM .........$95 DISHES 60m to 3.7m FROM ...........$130 15k –just leave out the two 1Ω resistors, and con­nect the positive lead from the cell holder to D1’s anode – see Fig.2. The standard discharge rate without components R1, R2 and Q2 in circuit is approximately 100mA. This is quite adequate for discharging AAA and AA size cells but should be increased to discharge larger cells within a reasonable time. Table 1 shows the components that you need to add to suit the various battery pack capacities. For example, adding R1 and Q2 increases the discharge rate to 150mA, while adding R2 as well increases it to 330mA. Finally, a 2.2V rail is required in order to accurately set the reference voltage applied to pin 2 of IC2a. This can come from a variable power supply or can be improvised using a couple of 1.5V batteries and a trimpot. Set the output voltage to exact­ly 2.2V, then connect the supply to the circuit in place of the nicad pack and adjust VR1 until the comparator just switches off. Note that this method of adjustment is necessary to compen­ sate for the voltage drop across D1. The reference voltage cannot be set using the method SC described previously. LOTS OF OTHER ITEMS FROM COAXIAL CABLE, DECODERS, ANGLE METERS, IN-LINE COAX AMPS, PAY-TV DECODER FOR JAPANESE, NTSC TO PAL TRANSCODERS, E-PAL DECODERS, PLUS MANY MORE For a free catalogue, fill in & mail or fax this coupon. ✍     Please send me a free catalog on your satellite systems. Name:____________________________ Street:____________________________ Suburb:_________________________ P/code________Phone_____________ L&M Satellite Supplies 33-35 Wickham Rd, Moorabin 3189 Ph (03) 553 1763; Fax (03) 532 2957 November 1994  67