12v circuit design

[subaro]

Re: 12v circuit design

just a quick thought here. when you have designed your delay discharge circuit and ready to test it, you can use a computer desktop power supply 12v for the output and you can monitor it while you are home. You have 12v to a capacitor with a resistor for slow discharge. ohms . use a fuse before the capacitor. Now you have to worry about burning down the house

realistically, those cameras draw very little current 300-700 milliamps, and the discharge circuit will be on for a very short time. you would be fine

[qbert69]

Re: 12v circuit design

Drop a current probe inline or external and give us the current require to power the device under load.If your thinking about a voltage devider resistor circuit you may not drop the voltage enough to get the current to power the device.You may need something like an LM 317 with a TO transistor case an heat sink???

I also recommend the LM317 circuit over the voltage divider circuit...Here is a simple circuit:

Versatile voltage regulator with LM317

The circuit is simple enough that once you get your resistance figured out, you should be able to do point-to-point soldering and encapsulate the circuit in epoxy for moisture resistance...don't encapsulate the heatsink though!

Depending on how much current the device draws, you may not need a heatsink on the LM317 IC. Don't forget heatsink thermal grease!

A great piece of cross reference software!:

NTE Electronics Inc | NTE QUICKCross Download

LM317 Datasheet:

http://www.nteinc.com/specs/900to999/pdf/nte956.pdf

PS--as an added note, if you have to use any capacitors, make sure you use the 105 C high temp caps for durability and longevity!

[DAG COPIERS & COMPUTERS]

Re: 12v circuit design

You guys know your electronics well. In designing your circuit do not overlook to calculate the circuit's C-R Time constant. Alternatively seek the services of an 'AUTO-Electrician?'

[allan]

Re: 12v circuit design

Car audio capacitor?

[NeoMatrix]

Re: 12v circuit design

You guys know your electronics well. In designing your circuit do not overlook to calculate the circuit's C-R Time constant. Alternatively seek the services of an 'AUTO-Electrician?'

You'll only require the R-C time if banginbishop still requires the camera to be turned off after a set periode. It's not coming off and A/C supply so there is no bridge rectifier. There shouldn't be any ripple voltage in/out of the LM317. Any electrolytic cap say 220ohms should work ok.

If he wires the camera in with the correct wiring procedure he will be able to turn the off camera instantly when he turns the ignition key off. No camera image data will be lost if its wired the correct way, as the camera will have a constant 12v supply.

The yellow wire should be connected to the ignition key on/off cycle; the red wire should go to the vehicle constant battery positive terminal; the black wire should be fixed to vehicle ground/chassis. If the camera works from a 12volt supply this is all he should be required to do. He shouldn't require a specially built circuit board.

[qbert69]

Re: 12v circuit design

Interesting thread here!....just wondering if removing the power from the camera will "corrupt" the video file if improperly truncated...or if the file is in a video format that would still be playable!