12V readout

K

kam

Member
Hi,

I am trying to read a ~12V DC supply and observe the voltage drop when a motor is turned on.

I wanted to see if i can read the voltage from a lipo battary pack on my RC CAR and if the voltage drops too low i can switch to the secondary battary.

Thought it be a good idea for a longer run.

Thanx
 
D

Dippy

Moderator
Are u asking about the electronics or coding?

Potential divider and maybe a little cap to smooth/filter glitches.

ReadADC or 10.
 
M

MFB

Senior Member
How about a relay that drops out at the lower voltage and switches the load over to the back-up battery? The relays inherent hysteresis may avoid any chatter when the main battery voltage increases as the load is removed.

A more exact approach would be to use a voltage comparator chip, with hysteresis feedback, driving a transistor or FET switch (if you really must, you could even replace the comparator with a PICAXE but why?).
 
K

kam

Member
Thanx for the quick response guys. I would like to eventually get the voltage readout wirelessly on Hyperterm or probebly have a few LEDs on my remote indicating the voltage level and also indicating when the Battary has been switched. so i think ADC will have to jump in. Now how exactly am i suppose to put 12V to a 08M without... poof:confused::eek:

I kinda got the idea of putting a comparitor chip but im new to this stuff

Kindly if i can get some detail instructions.

Thanx
 
M

MFB

Senior Member
Assuming that you are powering the PICAXE from a 5 volt regulator, you must limit the ADC input range to that level. This can be achieved by using two resistors in a potential divider network. One resistor goes between the 12 V line and the ADC input and the other resistor goes between the ADC input and ground. If the resistor to 12 V is 10K and the resistor to ground is 6.8K, then the PICAXE will see approximately 4.8V. These values of resistance should also provide protection against moderate over-voltage conditions.
 
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