Momentary to control on & off circuit

Thread Starter

25Raydo00

Joined Jul 30, 2019
10
Hi everyone. As stated I am trying to figure out the easiest way to make a momentary switch control button control the on and off for my 12V lights I have on my vehicle. I know the very basics of electronics, I currently have the lights powered by two different switches on relays. Longer story below
Basically I need the beginner way to make a momentary switch control a 12V (DC) system to turn lights on and off. I looked into latching circuits but it seems that can only be turned off by switching off the two position switch again.
Any links on tutorials or products needed to make this work are appreciated.


My main switch just turns the lights on or off by sending power to the relay
The second I have I am able to turn it on or off to make the Aux lights work with the high beams, flip it off they don't turn on with the high beams.
I want to do this as the vehicle is pretty new and I don't want toggle switches laying around. The "momentary switches" that I have are OEM that are normally used to control a momentary signal to turn traction control off. Just sends a signal to the BCM to shut it off. I want to do this because the car came with extra slots for the button so it will give me a nice factory look on the dashboard.
The push buttons themselves have 4 pins. Two for the light and two to control the switch.
my lights and relays are all 12 volt. The push buttons themselves do work on 12V kind of just hooked them up seeing if they would work.
Sorry for the long explatination, just new around here
 

dl324

Joined Mar 30, 2015
12,783
clipimage.jpg
This circuit from Popular Electronics circa the 1970's will do it.

If you provide more information about the load you're switching (I can't tell if it's lights or a relay), you'll get better information.
 

Thread Starter

25Raydo00

Joined Jul 30, 2019
10
Here's a full version using a LM555 driving a relay.
View attachment 233878
Just checking. The “lm555” when I look that up is a “555 timer IC” integrated circuit? Correct. Just trying to figure out so I can get everything to do this. I got the resistors picked out, switch out, and I got the relay picked out. The “2N2222” is a transistor. Correct?
 

Thread Starter

25Raydo00

Joined Jul 30, 2019
10
All correct.
What relay have you chosen?
I haven’t “chosen” one yet, sorry I meant to say I figured out where the relay was in the schematic. I’m assuming it doesn’t need to be a high amperage since it’s just controlling this circuit. Would I use a 4 or 5 pin relay?
 

AnalogKid

Joined Aug 1, 2013
9,151
What type of lights are being switched (incandescent, LED, other)?
What is the total current for all of the lights being switched at the same time?

The voltage and current being switched determine the type and size of relay needed.
The type and size of relay determine the relay coil current requirement.
The relay coil current requirement determines the type and size of the driver transistor.

ak
 

Thread Starter

25Raydo00

Joined Jul 30, 2019
10
What type of lights are being switched (incandescent, LED, other)?
What is the total current for all of the lights being switched at the same time?

The voltage and current being switched determine the type and size of relay needed.
The type and size of relay determine the relay coil current requirement.
The relay coil current requirement determines the type and size of the driver transistor.

ak
Halogens, I don’t have an exact amp draw. But ones very simmilar are 8 amp. I have four lights total. I am actually running two relays. With two lights on each switch because that’s how the harness came. 40 amp relays on the lights. This switch is just going to send power to those relays
 

Thread Starter

25Raydo00

Joined Jul 30, 2019
10
What type of lights are being switched (incandescent, LED, other)?
What is the total current for all of the lights being switched at the same time?

The voltage and current being switched determine the type and size of relay needed.
The type and size of relay determine the relay coil current requirement.
The relay coil current requirement determines the type and size of the driver transistor.

ak
Halogens, I don’t have an exact amp draw. But ones very simmilar are 8 amp. I have four lights total. I am actually running two relays. With two lights on each switch because that’s how the harness came. 40 amp relays on the lights. This switch is just going to send power to those relays
 

crutschow

Joined Mar 14, 2008
26,963
Here's the LTspice simulation of a similar PB alternate action circuit that uses two MOSFETs:
It will directly drive the relay coils, and comes up in the off-state when power is applied.
The MOSFETs can be just about any N-channel (M2) and P-channel (M1) devices.

As you can see the relay (green trace) alternately goes on and off for each push of the button (yellow trace).

Note that the circuit needs a small output load to operate properly.

1616981490505.png
 
Last edited:

sghioto

Joined Dec 31, 2017
2,328
I tried the above circuit using a BS250 for M3 with a 10K load. The only issue was if the supply voltage was applied through a switch the output was always High. Adding a 22nf from the gate of M2 to ground fixed the problem.
 

crutschow

Joined Mar 14, 2008
26,963
I tried the above circuit using a BS250 for M3 with a 10K load. The only issue was if the supply voltage was applied through a switch the output was always High. Adding a 22nf from the gate of M2 to ground fixed the problem.
Stray parasitics in a real circuit can cause differences in circuit operation compared to its simulation.
I will add that capacitor to my circuit to help insure correct operation in the actual circuit (below).
It has no noticeable effect on the simulation, but it should avoid the problem you noticed.

1616997824096.png
 
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