Power camcoder in car?

hiroc wrote:

Try this (view in fixed font or M$ Notepad): | | VCC | 1N4 + ______ | B+ 002 ___ | | | 8V+ | o->|-|___|-o-----o---|78M08|---o---------o----o---o | 2.2 | +| |_____| +| | | | /-/ --- | --- .-. .-. | 6PKE18 ^ --- | --- | | | |1.2K | o | 10uF| | 10uF| 10K| | | | | B-| | | | | '-' '-' | === === === === === | | | GND GND GND GND GND '-----o |LED1 | | | V~ | .--------------------' .-. -~ | | | | | | | VCC 18| | | | | + '-' | | | VCC LED2| | | | | + V~ === | | | |\\| -~ GND | | '--|+\\ ___ | | | | >-|___|---' | | .--|-/ 2.2K .-----o---o | | |/| | | 8V- | | === | .-. | | GND |0.22| | | | 1/2 LM393 | | | | '-------------------------' '-' | | | === | GND | (created by AACircuit v1.28.5 beta 02/06/05

All of these components are easily available at Mouser.com for a few bucks.

Here's how it works: The diode, 2.2 ohm resistor, and Transzorb help protect the rest of the circuit from load dump or reverse polarity. Your 78M08 will give you 8V (close enough -- even if it's a little high, that would be similar to a fully charged battery). The trick is the current sense resistor on the 8V return line. A small voltage is impressed across it, which is sensed by the comparator. The comparator output will turn on the LED if total current (LED + camcorder) goes over 60mA or so.

Note that you will need high intensity LEDs for this circuit, because the LED current limit resistors are set for 7mA each. If you want to use standard LEDs, and you get false triggering, bump up the 18 ohm resistor a little bit.

This isn't the most elegant circuit, but it will work OK and be safe for your camcorder. Be sure to remember that the voltage source for the camcorder should be isolated from car chassis ground -- the negative is not at ground potential.

Good luck Chris

I must use car battery!! I is only voltage source in the car

Hi, Hiroc. Connect the car battery to the terminals marked B+ and B-.

Sorry -- I should have been more clear on that. This *is* made to work with a car battery.

Cheers Chris

Thanks!

Hey, Hiroc. Looking back, I saw I marked the linear regulator as a

78M08 -- you should use a 7808. This will give you 1 amp capability instead of 1/2A with the M08.

Also, be sure to put a heat sink on the regulator -- it may dissipate over 4 watts when the car is running (battery voltage at 14V or so).

This should be OK as long as you're not running backlighting.

Good luck Chris