View Full Version : Hacking a LED voltimeter + thermometer to test battery with alarm

02-06-2014, 11:57 AM
Hi everyone, I was wondering if it would possible to hack one of those cheap LED voltimeter + temperature modules http://www.ebay.com/itm/0-56-33-200V-LED-Digital-Gauge-DC-Car-Volt-Meter-Temperature-Voltage-Time-3in1-/190965349050?pt=LH_DefaultDomain_0&var=&hash=item2c766bfaba, to send its data to an Arduino, so we can use it to turn on buzzer alarms when our battery is running low or if the temperature is too high. Any ideas?

Would it be easier to just create a self made voltmeter and use a temperature sensor instead?

02-06-2014, 04:19 PM
Your Arduino has analog pins. Create a resistor divider to get the voltage down to the level within spec of the A/D port, and check it periodically. Temperature sensors are cheap and easy to interface to.

02-06-2014, 10:50 PM
Yes; a LM34DZ for temperature is $2.52 at Digi-Key: http://www.digikey.com/product-detail/en/LM34DZ%2FNOPB/LM34DZ%2FNOPB-ND/32485
Two resistors (say, 22 kOhm to analog pin, and 4 kOhm from that pin to ground) makes for a good voltage divider, making about 1V analog per 5V on the battery (so 1000 in means approximately 25V battery; 200 in means approximately 5V battery.)

02-14-2014, 06:21 AM
Yes, you are right, after seeing how difficult would be to reprogram it, using components is the best choice. I just wanted to try to set something easy and compact using already made components, but sometimes that's not the best idea. Thank you guys.

03-09-2014, 12:39 PM
Hi everyone, I've received the voltmeter and I find them not so good for less than 4V :( So defintely not the way to go with so many complications and limitations. I'll let you all know how the battery gauge for powered wheelchairs go in the project thread. Thanks :)