555 Touch Switch

This touch switch built based on famous 555 timer IC. When the plate is touched the 555 timer is triggered and the output on pin 3 goes high turning on the LED and the buzzer for a certain period of time. The time that the LED and the buzzer is on is based on the values of the capacitor and resistor connected to pin 6 & 7. The 10M resistor on pin 2 causes the the circuit to be very sensitive to the touch.

555 Touch Switch

Maximite Stepper Motor Interface

This simple circuit and program listing allows the Maximite microcomputer (SILICON CHIP, March-May 2011) to control a stepper motor. It could be expanded to allow for the control of multiple motors, with four of the Maximite’s external I/O pins used to control each motor with identical driver circuits. A ULN2003 Darlington transistor array (IC1) switches current through the stepper motor’s two windings in either direction. When one of the four Maximite output pins (8, 12, 16 & 20, corresponding to I/Os 19, 17, 15 & 13) goes high, the corresponding output pin on IC1 goes low, sinking current through a motor winding. Conversely, when these pins are high, the corresponding Darlington transistor is off and so no current flows through that portion of the winding.

Maximite stepper motor interface Schematic

IR Remote Switch

Imagine the convenience of selecting TV channels using your remote and then pointing the same remote to your switchboard to switch on/off the fan or the tubelight. Here is a simple circuit to remotely switch on/off any electrical device through a relay using the normal TV/VCR/VCP/VCD remote control unit. It works up to a distance of about 10 metres. The circuit is built around a 3-pin IR IC receiver (Siemens SFH-506-38 or equivalent) that can detect 38kHz burst frequency generated by a TV remote. (This IR receiver module has been covered earlier in many projects published in this blog.) The output pin of IR sensor goes low when it detects IR light, triggering the monostable (1-second) built around timer NE555. The output of the mono toggles the J-K flip flop, whose Q output drives the relay through SL100 npn transistor (T1).

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Infrared Remote for Toy Car Motor Controller

This add-on circuit enables remote switching on/off of battery-operated toy cars with the help of a TV/video remote control handset operating at 30–40 kHz. When the circuit is energised from a 6V battery, the decade counter CD4017 (IC2), which is configured as a toggle flip-flop, is immediately reset by the power-on-reset combination of capacitor C3 and resistor R6. LED1 connected to pin 3 (Q0) of IC2 via resistor R5 glows to indicate the standby condition. In standby condition, data output pin of the integrated infrared receiver/demodulator (SFH505A or TSOP1738) is at a high level (about 5 volts) and transistor T1 is ‘off’ (reverse biased).


Gas Leakage Alarm

 LPG gas leakage detector with audio visual indicator

LPG gas is supplied in pressurized steel cylinders. As this gas is heavier than air, when it leaks from a cylinder it flows along floor and tends to settle in low spots such as a basement. This can cause fire or suffocation if not dealt with.

Here is a circuit that detects the leakage of LPG gas and alerts the user through audio-visual indications. Fig. 1 shows the circuit of the gas leakage alarm. The circuit operates off a 9V PP3 battery. Zener diode ZD1 is used to convert 9V into 5V DC to drive the gas sensor module. The SEN-1327 gas sensor module from RhydoLABZ is used in this circuit. Its output goes high when the gas level reaches or exceeds certain point. A preset in the module is used to set the threshold. Interfacing with the sensor module is done through a 4-pin SIP header. Pin details of the gas sensor module are shown in Fig. 2.

Home Appliance Controller Using TV Remote

Switch home or industrial appliance On/Off with TV remote control

This circuit is designed to switch on/off any home or industrial appliance by using the TV/DVD remote controller. The circuit can be operated up to a distance of 5-10 metre depending on the remote used. The circuit consists of a step-down transformer X1 (6V-0-6V, 250mA secondary), 5V regulator 7805 (IC1), two 5V, 1 change-over (C/O) relay, a timer NE555 IC (IC2), an IR receiver module (IRX1 TSOP1738) and some discrete components. The circuit works on regulated 5V, which is derived from X1 and regulated by IC1. Home appliance is controlled either by pressing any key on the remote or by manually pressing switch S1 to ‘on’ state.

Home Appliance Control Using TV Remote
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Bicycle Horn Using Tone Generator KA2411

An interesting circuit of a bicycle horn based on a popular, low cost telecom ringer chip is described here. This circuit can be powered using the bicycle dynamo supply and does not require batteries, which need to be replaced frequently. The section comprising diodes (D1 and D2) and capacitors (C1 and C2) forms a half-wave voltage-doubler circuit. The output of the voltage doubler is fed to capacitor C3 via resistor R1. The maximum DC supply that can be applied to the input terminals of IC1 is 28V. Therefore zener diode ZD1 is added to the circuit for protection and voltage regulation. The remainder of the circuit is the tone generator based on IC1 (KA2411).

Bicycle Horn Using Tone Generator Schematic