View Full Version : How do I make an LED VOLT METER
ultimods
12-29-2007, 05:03 PM
Hi all, I have been watching systm for a while now and thought this would be a good place to come and ask a few questions. Currently I am building a controller for guitar hero / Frets on Fire. I was wanting to put a meter on my guitar telling how much battery power is left. I have a 4.7V battery pack. So the meter would measure from 4.7V down. Does anyone know how I can build this? Or buy one? And another thing Patrick, You think you could do a podcast on making one???
scienceking
12-29-2007, 06:55 PM
I have a 4.7V battery pack. So the meter would measure from 4.7V down. Does anyone know how I can build this? Or buy one? And another thing Patrick, You think you could do a podcast on making one???
I made one a couple months ago. Most microcontrollers have at least once input channel with an Analog to Digital converter subsystem. So just use that(read the docs on how to use the AtoD) to sense the voltage, and then use the micro outputs and an LED driver chip method of your choice to output to the LED 7seg. Or if you just want one "low" LED, it would be even easier, and would require nothing but your micro. I've never used the AVR before, but I'm pretty sure they have a model that has an input AtoD that you can use to do this quite easily, and there is a tutorial episode of systm to get you started with that.
The more elegant way to make a battery low indicator is to use a single BJT inverter set with a q-point that will drive a logic low if the base voltage is above a certain voltage, and then to run that into a digital inverter to drive your LED. You can even do it with just the BJT, but it would be more difficult to make your response curve steep enough to make it so the LED wouldn't become sorta dim near your cutoff point instead of cleanly going from on to off.
ultimods
12-31-2007, 05:56 PM
which episode of systm is there??? And does anyone sell anything like this??
Would something like this work?? : http://store.qkits.com/moreinfo.cfm/FK101
And here is my blog for the guitar hero controller: http://ultimods.hyperphp.com
commandergc
01-01-2008, 07:39 PM
Since you only need to measure 4.7v you should have a look at using the LM3915 chip.
http://www.national.com/mpf/LM/LM3915.html - this page has some usage diagrams that may do what you need!
The smallest picaxe (8 pins) and a handful of led's/resistors/caps is all you'd need, the shipping would probably cost more than the parts(~ $5). These things spank the AVR and the BStamp on entry level ease of use, interchangeable pinout between models(easy upgrades), included feature set, and price.
Info:
http://en.wikipedia.org/wiki/PICAXE#See_also
http://dave.fraildream.net/picaxe/px08io.shtml
http://www.hippy.freeserve.co.uk/picaxeqa.htm
http://www.rev-ed.co.uk/picaxe/ <===RTFM and follow the tutorial to get the ADC up and the light out.