4013 Based Momentary Switch is Random ??

[ozhummer]

Hi,

Refer to the attached schematic (a snippet of the entire circuit) - This is basically a relay driven momentary switch that just toggles ! - Really simple.. The 100R and 47uf provide a bit of protection against power spikes etc. This circuit forms part of an automotive accessory.

MY PROBLEM IS!

The unit operates from the acc power supply in the vehicle. But when the acc is turned on, the state of the switch is totally random ! - sometimes on, others off ..


Can anyone suggest a modification or something that will ensure it is always off when power is applied ???

Thanks in advance
KD

 

[ericgibbs]

Hi,

Refer to the attached schematic (a snippet of the entire circuit) - This is basically a relay driven momentary switch that just toggles ! - Really simple.. The 100R and 47uf provide a bit of protection against power spikes etc. This circuit forms part of an automotive accessory.

MY PROBLEM IS!

The unit operates from the acc power supply in the vehicle. But when the acc is turned on, the state of the switch is totally random ! - sometimes on, others off ..


Can anyone suggest a modification or something that will ensure it is always off when power is applied ???

Thanks in advance
KD

hi,
Use the 'R' RESET pins of the 4013.
As it requires a positive reset pulse use a 10nF thru 47nF from +V to the R pins and a 10k thru 47k from 0V to the R pins [link the two R's together] so that you just have one Res/Cap...OK?

 

[ozhummer]

Tried this - but still appears to be pretty random....

 

[Grossel]

I think I see the problem.

The supply voltage for the cd4013 is not directly connected to source, but rather through a 100R resistor. So when the relay activates, supply voltage will drop. This may be resolved by replacing C7 with a bigger cap, or if main power supply is stable, just bypass R9 (see atachment)

I guess having analog voltage into a clock input on a 4013 would make it unstable. Capacitor C3 will cause voltage into CLK input to increase relatively slowly after pressing the switch. Putting a schmittrigger between should help.

 

[Diver300]

I have a couple of suggestions. You should run the relay directly from the 12 V and the CD4013 from the 100 R resistor and the capacitor. The 100 R resistor would probably stop the relay from working.

If you put a diode in series with the 100 R resistor, and change Q1 to a MOSFET, the current draw will be just about nothing and capacitor will keep the CD4013 running for at least several hours. Or, you could just power the CD4013 from a permanent supply on the vehicle, and the relay from the ACC supply. That way, even if it turns on in a random state, you only have to worry when you disconnect the vehicle battery.