Need help finding resistance for 12V to get 300 mA.

[Ricky Spartacus]

Assuming an ignition control module's trigger input can't exceed 300 mA,
what should resistor value to trigger this device with 12V. I've triggered
this device with 1.5V cell and works fine but not sure how to do the math
regarding the question above. I lost the website that has a current
calculator.
Ric

 

[Brian]

Assuming an ignition control module's trigger input can't exceed 300 mA,
what should resistor value to trigger this device with 12V. I've triggered
this device with 1.5V cell and works fine but not sure how to do the math
regarding the question above. I lost the website that has a current
calculator.
Ric

Why not have your own program that can do that (plus a lot more), for less
than the price of a good technical book. See what I mean at
http://www.fncwired.com

It has a demo that you can download.

R = E / I
P = E * I

R = resistor value
E = volts
I = current
P = Power rating needed for resistor

12 / .3 = 40 ohms
12 * .3 = 3.6 watts

Hope this helps,
Brian

 

[Indian Summer]

40-Ohm, 3.5999999999W

http://www.opamplabs.com/eirp.htm

 

[Rich Grise]

Can you post the specs on that module? I can't imagine something
designed for a car that would be damaged with up to 12 volts at
the input. The spec _might_ be saying that the input won't load
your driver circuit more than 300 mA. I don't know if anybody's
ever seen a spec for an input where the drive to that input has
to be current-limited.

Thanks,
Rich

 

[Ricky Spartacus]

Hello Rich,

Spec sheets are hard to find but I can say that the input takes 5V. I
just dreamed up the 300mA idea from somewhere. You can try looking at
the picture of the module circuit itself. This pic is from a Toyota.

http://autotails.tripod.com/s.gif

This from a Honda/Rover.

http://autotails.tripod.com/rov-rgn0.gif

Same pic as above.

http://autotails.tripod.com/rov-rgn1.gif
Ric