I am trying to make sure that my PNP circuit is correct to be able to use a source ground to trigger a 12v automotive backup camera to change views (5 views in sequence when momentary power 12v is applied). I am using source power from my cigarette lighter (15A) and want to make sure that I have calculated the math correctly to make the circuit work. The backup camera does not specify a REQUIRED current to change the view of the camera but the instructions do mention that most installers use a 12v ignition switched power from the cigarette lighter. I have a TIP42C PNP transistor and want to make sure that I wire it up correctly. I am using the attached schematic as my design but need to verify that the R1 and R2 calculations are correct.


I have: R1 should be 2.4 Ohms and R2 should be 10 times R1 at 24 Ohms.

R1=12v/5A
R1=2.4 Ohms

When I ground the base, a 5A current should flow from the Emitter to the Collector sending 12v (5A) to the backup camera trigger wire to change views.

Any flaws with this design?

I don't want any "back current" flowing towards the ground on my base lead as this trigger ground goes to the ECM of my vehicle.

Thank you for advice in advance!

 

I am trying to make sure that my PNP circuit is correct to be able to use a source ground to trigger a 12v automotive backup camera to change views (5 views in sequence when momentary power 12v is applied). I am using source power from my cigarette lighter (15A) and want to make sure that I have calculated the math correctly to make the circuit work. The backup camera does not specify a REQUIRED current to change the view of the camera but the instructions do mention that most installers use a 12v ignition switched power from the cigarette lighter. I have a TIP42C PNP transistor and want to make sure that I wire it up correctly. I am using the attached schematic as my design but need to verify that the R1 and R2 calculations are correct.
View attachment 119680

I have: R1 should be 2.4 Ohms and R2 should be 10 times R1 at 24 Ohms.

R1=12v/5A
R1=2.4 Ohms

When I ground the base, a 5A current should flow from the Emitter to the Collector sending 12v (5A) to the backup camera trigger wire to change views.

Any flaws with this design?

I don't want any "back current" flowing towards the ground on my base lead as this trigger ground goes to the ECM of my vehicle.

Thank you for advice in advance!

Why are 5A needed just to toggle a multiplexer to change camera views? That seems like something that needs 5 milliamps. Or, virtually no current flow, just a positive voltage to trigger.

R1 of 2.4 ohms should burn the base of nearly every transistor out there.

I think you mean R1 should be 1k and R2 should be 10k or 100k.

 

This is why I am posting here. I couldn't understand why the camera takes it's 12v momentary switch trigger from the cigarette lighter! You are likely right in that all the camera needs is switched 12v with little to no current.

 

This is why I am posting here. I couldn't understand why the camera takes it's 12v momentary switch trigger from the cigarette lighter! You are likely right in that all the camera needs is switched 12v with little to no current.

I'm not intentionally meaning to be rude / unkind, but if instead of just posting what might be a flawed circuit and asking for help on how to fix it, you'd make it easier for all of us if you'd post the camera's data sheet, tell us what it is you want the camera to do, and let us get on with it.

 

Thank you. Certainly not a rude comment. All input is welcome so long as it is constructive.

The only specs I have for the backup camera is 12v <70mA.

12v momentary trigger to the multiplexer to change the views.

Rather than use a 12v positive momentary switch, I am trying to use a toggle switch on my tiptronic transmission shift lever (grounding switch) to trigger a circuit to supply the required positive 12v for the backup camera duplexer to switch views.

 

R2=10k R1=1.5K
Add a 1.5K from collector to ground to drain any leakage current.

 

Thank you. Certainly not a rude comment. All input is welcome so long as it is constructive.

The only specs I have for the backup camera is 12v <70mA.

12v momentary trigger to the multiplexer to change the views.

How did this multiplexer suddenly come into being:?

Rather than use a 12v positive momentary switch, I am trying to use a toggle switch on my tiptronic transmission shift lever (grounding switch) to trigger a circuit to supply the required positive 12v for the backup camera duplexer to switch views.

All nonsense, since you can't post a schematic defining what you're talking about.

 

You are basically on the right track- but the current levels you suggest are probably way too high.

The camera is looking for a signal 0-12V? You could design for 100 milliamps and it should work fine.

 

Okay. That's what I couldn't get my head around. It seemed WAY too high! I'll set it up for 100mA and try it. Thanks for all the input.