[SOLVED] Intermittent wiper control resets when indicators or horn are turned on

[SohailChamba]

I built a astable multivibrator using two npn transistors. I then used this circuit to drive my car's wiper. Apparently circuit works fine and turns the wiper after about 5 seconds. But when I on the left or right indicators or honks the Horn, the timing of the circuit is disturbed. Circuit is given below. You are requested to correct the circuit.

https://obrazki.elektroda.pl/8570938100_1394434418.jpg

Parts used are
R1 = 10K, R2 = 100 K R = 220 Ohm
C1 = C2 = 100 uf
Q1 = Q2 = C945

 

[chuckey]

Feed the Vcc from the +12 V line via a 10 ohm resistor, connect a 470 MFD capacitor from the Vcc line to earth. The circuit is very sensitive to voltage changes and spikes on the +12V line, so a bit of added decoupling might sort it out. There should be a diode connected across the relay coil, otherwise when it de-energises it produces a voltage spike which can blow up the transistor.
Frank

 

[SohailChamba]

Feed the Vcc from the +12 V line via a 10 ohm resistor, connect a 470 MFD capacitor from the Vcc line to earth. The circuit is very sensitive to voltage changes and spikes on the +12V line, so a bit of added decoupling might sort it out. There should be a diode connected across the relay coil, otherwise when it de-energises it produces a voltage spike which can blow up the transistor.
Frank

Hello Frank, Thankyou for your reply to my question. I edited the circuit as you proposed. I added a capacitor across +ve and gnd, fed the Vcc via 10 ohm resistor and added a revers biased diod across the relay. But the problem is still there.

What can I do next with the circuit?

 

[chuckey]

If its not spikes travelling down the +12V line , it must be a problem with earthy side. The switch to energise/disenergise this circuit is not shown. Could it be that this lead and circuit are sharing the same earth as the horn and indicators? like a wire running down from the steering wheel stalk cluster?
Frank

 

[SohailChamba]

Certainly the Intermittent controller, indicators and horn share the same earth. The +ve line of the circuit is switched. Will adding a reverse biased diode across the supply voltage work?

 

[FvM]

I think the problem is a bit more basic.

The simple circuit isn't prepared for the supply voltage drops generated by heavy loads. The supply filtering suggested by chuckey is pointing in the right direction, but longer voltage drops will be still affecting multivibrator operation.

A more rugged solution would separate the oscillator part from the relay driver or use an oscillator circuit that is less sensitive to supply variations.

 

[betwixt]

Might be worth trying a diode instead of the 10 Ohm resistor, cathode end to the multivibrator and still using the 470uF capacitor. The diode will allow current in to power the oscilator but prevent the capacitor discharging back into the car wiring.

Brian.

 

[SohailChamba]

Hello Betwixt your proposed solution worked. Now the horn, indicators and my wiper controller are separated. Thanks for the solution. And hats off to chuckey who identified the problem.