Infrared remote receiver has four outputs

This circuit enables any infrared (IR) remote control to control the outputs of a 4017 decade counter.

It's quite simple really and uses a 3-terminal IR receiver (IRD1) to pick up infrared signals from the transmitter. IRD1's output is then coupled to NPN transistor Q1 via a 220nF capacitor.

Transistor Q1 functions as a common-emitter amplifier with a gain of about 20, as set by the ratio of its 10kΩ collector resistor to its 470Ω emitter resistor. Q1 in turn triggers IC1, a 4047 monostable which in turn clocks a 4017 decade counter (IC2).

Basically, IC1 provides a clock pulse to IC2 each time a remote control button is pressed. If you don't wish to use all 10 outputs from IC2, simply connect the first unused output to pin 15 (MR).

In this case, only the first four outputs (O0-O3) of the counter are used and so the O4 output is connected to pin 15 to reset the counter on the fifth button press.

Power for the circuit is derived from the mains via a transformer and bridge rectifier which produces about 15-27V DC. This is then fed to 3-terminal regulators REG1 & REG2 to derive +12V and +5V supply rails.

Fred Edwards,

Ardross, WA. ($35)

Wide-range inductance meter Looking for a wide-range inductance meter? This circuit can measure inductors ranging in value from a few microhenries (mH) up to one Henry (1H). NAND gate IC1a, crystal X1 and their associated components form a 2MHz oscillator. Its output is divided down by BCD counters IC2-IC4 (4518) to produce six test frequencies: 1MHz, 100kHz, 10kHz, 1kHz, 100Hz and 10Hz. These are then fed to two 4066 quad bilateral switches (IC6 & IC7). As well as clocking IC2a, the 2MHz output from IC1a also clocks decade counter IC5 (4017). When a range select button is pressed, IC5's corresponding output (O0-O5) quickly goes high. This output in turn activates its corresponding bilateral switch to switch through the selected test frequency. Parallel NAND gates IC1c & IC1d buffer this test frequency which is then fed via S1a and an 8.2Ω resistor to the gate of Mosfet Q1. As a result, when S1 is in the "MEAS" position, Q1 turns on and off at the test frequency and current pulses flow through the test inductor (via S1b and a 1kΩ series resistor). Each time the current switches off, a back-EMF voltage is generated by the inductor. This voltage is then rectified and applied to a 100μA meter via VR1 and D7 (a BAT42 high-speed Schottky diode). Because back-EMF is proportional to inductance, the meter can be calibrated against a known inductance by adjusting VR1 until the correct reading is obtained. The remaining ranges are then automatically calibrated. Finally, the test inductor can be checked for continuity be switching S1 to the "CONT" position. Provided the coil is OK, this turns on transistor Q1 and allows current to flow via a 4.7kΩ resistor to light LED1. Gregory Freeman, Mount Barker, SA. ($50)

Simple circuit charges up to 12 NiCds

This handy circuit can be used to charge from one to 12 NiCd cells from a car battery. Up to six cells can be charged with switch S1 in the "normal" position. The LM317regulator operates as a simple current source, providing about 530mA when R1 = 2.35Ω (two 4.7Ω resistors in parallel).

For more than six cells, S1 is set to the "boost" position. This applies powers to IC1, a 10W (or 20W) audio power amplifier. Positive feedback from its output (pin 4) to non-inverting input (pin 1) causes IC1 to act as a square wave oscillator. This square wave signal is coupled to the junction of Schottky diodes D1 and D2 via a 330μF capacitor, forming a conventional charge-pump voltage doubler. Over 20V (unloaded) appears at the input to REG1 - enough to charge a maximum of 12 cells!

SILICON CHIP.

 

Simple knock alarm with piezo sensor This circuit uses a thin piezoelectric sensor to sense the vibrations generated by knocking on a surface; eg, a door or table. Basically, it amplifies and processes the signal from the sensor and sounds an alarm for a preset period. In operation, the piezoelectric sensor converts mechanical vibration into an electrical signal. This sensor can be attached to a door, a cash box, cupboard, etc using adhesive. A 1-1.5m long shielded cable can then be connected between the sensor plate and the input of the circuit. The signal generated by the sensor is amplified by transistors Q1-Q3 which are wired as common-emitter amplifiers. The signal is then rectified by diode D1 and amplified by transistors Q4-Q6. As shown, the output from Q6's collector is fed to pin 4 (reset) of 555 timer IC1. This is wired as an astable multivibrator. Each time Q6 turns on, its collector goes high and IC1 activates and produces an alarm tone in the speaker. The alarm automatically turns off 10s after knocking ceases - ie, the time taken for the 22μF capacitor on Q4's emitter to discharge. Finally, note that it may be necessary to adjust the 470Ω resistor in Q6's collector circuit to ensure that IC1 remains off in the absence of any perceptible knock. A value somewhere between 220Ω and 680Ω should be suitable. Raj. K. Gorkhali, Kathmandu, Nepal.

Gym agility: a simple strategy game

This simple circuit is a two-person game of strategy and speed - and potentially, agility and athletic fitness.

Each player has a row of four LEDs before him/her. Beside each LED, there is a pushbutton which, when pressed, lights up the corresponding LED. The aim of the game is for a player to illuminate all four of their LEDs in a row, in which case the circuit declares a winner.

However, there is a catch. As soon as you light one of your own LEDs, the other player's corresponding LED goes out - and vice versa. The game begins by giving each player two illuminated LEDs.

Consider now that this game is scaled up and used in a gym. If the LEDs in the circuit are directly replaced with N-channel power MOSFETs, then 12V globes can be illuminated (a MOSFET's gate is wired in place of a LED's anode, the source goes to negative, and the load is wired between the drain and positive).

If four large pushbuttons are mounted on one wall and four on another, this could become a game of agility - if not a physical tussle to keep the other player away from critical pushbuttons.

Here's how the circuit works: Schmitt NAND gate IC1a and IC1b (4093) form a simple bistable latch. When one output (pin 3) goes "high", the other output (pin 4) goes "low" and vice versa. The main advantage of using a bistable latch (as opposed to a flipflop) is that it does not suffer from switch bounce.

Four such bistable latches are fed to inputs A-D of IC2. However, for the sake of simplicity, only one of these is shown; ie, IC1a-IC1b.

We now need to identify when all four bistable latches go either "high" or "low". This is done using IC2, a 4067 16-channel multiplexer. When inputs A-D are all "low" (binary 0000), this opens decimal channel 0. Conversely, when all are "high" (binary 1111), this opens decimal channel 15. Channels 0 and 15 thus trigger a win for one side or the other, by taking pins 9 or 16 of IC2 "low".

Finally, if the game is quite hectic, a win might only last for a fraction of a second before it is lost again. Therefore, IC1c and IC1d are wired as timers, which do not permit any further play until a win has been reported for one or two seconds - either via LED3 or LED4. During this time, however, the players' buttons may be pressed to reset the game to two LEDs all.

Thomas Scarborough,

Capetown, South Africa. ($35)

Adding a 100V line transformer to the SC480 amplifier This circuit shows how to use the SILICON CHIP SC480 amplifier module to drive a 100V line transformer for PA work. The output of the amplifier directly drives the primary of the transformer, with the secondary then providing the 100V line output. Diodes D1 & D2 are included to protect the transistor output stage against back-EMF spikes which can be generated by the transformer if the amplifier is driven into clipping. Note: the specified Altronics 100V line transformer has a primary DC resistance of 4Ω which lets it work satisfactorily with the amplifier's likely DC output offset of around ±30mV. The SC480 cannot be used with any line output transformer which has a primary resistance of less than 1Ω. SILICON CHIP.

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