Battery Monitor for RoboQuad

This is my first mod for the RoboQuad: a battery monitor. When properly adjusted, it will visually tell you when your batteries are geting low. This mod stays on at all times. The drain on the batteries is very minute; it's around 0.02uA. This mod requires soldering and making a circuit board for the monitor, but it is a very easy circuit to build.

NOTE: If you do not understand soldering and reading schematics, find someone to help you build it or don’t attempt this mod.

So, lets get started! First, let's build the board. In this picture is the schematic for the monitor. Notice that there really aren't many parts. All parts can be substituted with like parts.

For the LED, I used a blinking LED; I thought it would look cooler than just a steady light. The list of parts are as follows: R1,R2 – 100 ohm resistor ¼ watt; R3 – mini 10K Variable resistor; D1 – 1N4733A 5.1 Zener Diode or any 4.3 to 5.1 ZD; D2 – LED (any color; I used a red blinking one); Q1 – 2N3904 or 2N2222 NPN general purpose transistor. Misc : wire, solder, soldering board, wire clippers, etc.

Finnished Board

As you can see, it's small. The wires that have tie straps on them are as follows: red and green are for the LED and red and black are for the battery connection @ 6V. As a reminder, this circuit is designed to run even when RoboQuad is turned off. It functions as a reminder; if you shelf it for a long time, you can see that you did not take his batteries out of him. Once you have built the circuit, it is time to test it out. Attach the power to an adjustable power source and set it to 6 volts and attach the power and the ground to the circuit. If all goes well, your LED should light or blink whichever LED you put in. If it does not light, move the VR "R3" all the way to the right and then to the left and check the LED for light. If there is no light, you can recheck your wiring. Now that your LED is on, adjust your power to, or around, 3.26V; this is the threshold you want before changing or replacing your batteries. Now, adjust the VR until the light turns out. Your adjustments are complete. Lock down the VR "R3" with some hot glue so that it won't turn. You should not have to make this adjustment again. Now that you have made the adjustments, it's time to cover the circuit from any damage or shorting out. If you made the PCB the same size that I have, which is from the hole count on the board 10x9 at the cut, place a piece of heatshrink tube 1" size over it and heat it down over the circuit.

Note: make sure that you have no bad or cold solder joints before you do this.


Now, let's drill the hole for the LED; you can pick any spot that you want, but I put mine next to the left of the switch. Use a 3/16" drill bit and you may need to open the hole just a little bit for a good tight fit.


Next, trial fit your LED. If it won't go in, open the hole a little bit more.

LedTrial Fit

Don't worry about that switch that you see in the photo, I was doing 2 mods at the same time. If your LED fits tightly, then you won't have to hot glue it down. I made it like this so the LED and body can be easily removed. Next comes the attaching of the power lines; how you do this is up to you. You can attach the red 6 volt line to the connector of the battery; or, you could attach it like I did by cutting the orange wire on J1 of the main circuit board connector and the black wire "Ground" also on J1, and the wire is black also. The red wire on J1 is your 3V power line; we will not be using this one, so don't cut it. Once cutting and soldering is complete, make sure you heat shrink the wires or electrical tape them.


The next step is to secure your battery monitor mod board. I placed it behind the back right motor (it fits like a glove in that position) and hotglued it down.

BMMB Glueing

The only thing left is to secure and tuck away the wires. Use tie straps to hold the wires togeather and tuck them under the cavity where the back LED is located, then guide the wires from the circuit down the side of the motor. Be sure not to cover any of the screw holes. Once this is done, reassemble your Quad and install the batteries. When the LED no longer blinks or lights, the batteries need replacement.

wires tucked

I will post a video when my RoboQuad is back together. I hope that this mod helps you determine when you need to replace the batteries, and also as a reminder to take them out when storing it. I am looking foward to sharing more of my mods and hacks with everyone. Until then, enjoy!



milw's picture

hey GWJax, nice article! I'll definitely do this one as soon as I get my Roboquad!

cheers- Scott 

markcra's picture

Fantastic article. Nice simple circuit and useful in so many applications.

GWJax's picture

Thanks, I'll have more to come.


Nocturnal's picture

Nice. I am curious though, how the current draw can be only 0.02uA when you are powering an LED.

GWJax's picture

I used a blinking LED which changes the current at diffrent intervals and it averaged out to 0.02uA or at least that is what my meter read. I'll double check it with the Multi Sim 8.0 software and read it from the simulation and get back at ya.  GWJax

milw's picture

Just from inspection of the schematic, you've got a 10,100 ohm path to ground from your 6 V supply. From I=V/R, I get I=6/10,100 or 0.59 milli Amps, thats more on the order of 600 micro Amps. And of course, that's not counting what is going through the LED (It might well be an ultralow power LED, but the bias circuit is always going to be draining some power from the batteries.)

GWJax's picture

OK on the simulation this is the following: the LED is pulling between 7.970pA to 7.995pA the transistor from the Collector is 7.965pA to 7.950pA the Emitter is -6.265pA to -6.295pA and Base is -1.655pA to -1.695pA and in the rough with a standard LED you should be pulling about 283.0 mV from the circuit and if you use a blinking led the circuit will pull about 1/3rd less because it is like a switch turning the power on and off from the collector to the emitter. these reading was pulled off using CircuitMaker 2000 Pro not MultiSim8 Pro, sorry I have both. GWJax

Nocturnal's picture

Do you have a datasheet for the LED you used?

GWJax's picture

No I do not, It was in one of my junk piles. Sorry. But any Blinking LED should work just fine.

GWJax's picture


When the mod is in, keep an eye out for the LED flashing or steady LED while the quad is in the running mode. Due to its design, I did not consider the current drop while the bot is running. While the Quad is running this is a great time to payclose attention to the monitor. if the LED goes out when making a turn or walking then the batteries are close to being replaced. Sorry for that little mistake. when the bot is at a stand still or spleep mode the LED will be bright, unless the battries are just dead under a combined voltage of 3.26Vs. Let me know if anyone has tried this mod and your results. If I have to change it just let me know PM or postit and I'll get it. Thanks again for looking. And if you wan't more mods which a program memory stay control is on it way, just ask for it. GWJax

RobosapienV2-4mem8's picture

Nice mod GWJax. I was also concerned about the current draw of 0.02uA, But you seemed to have resolved that issue.

GWJax's picture

Thanks for the comment RobosapienV2-4mem8. I too was woundering about the current draw that I read and checked again with 3 other meters and all stated the same. So I pluged it into the simulator and found the answers. Thanks for looking. GWJax

roschler's picture

Resurrecting the thread. :)

Nice mod GWJax. I got stuck mid-project with my Roboquad, right after the Skype/Voice control demo I did. I bought an IR based power switch that ran on batteries and also a version of the X10 PowerMid (Infrared signal repeater) that runs on batteries from the UK. For some odd reason X10/USA only manufactures units that require A/C power but the UK units can run on AC or batteries.

My intent was to put the battery powered X10 receiver on the Roboquad's back with the extender cord placing the IR output right in front of his receiver; for perfect wireless transmission (no line of sight issues anymore). The IR based power switch, which Rovio would tow in a little cart behind it, would turn power on to the X10 receiver and the analog camera/mic on Rovio's head so they would consume power only when I was calling in to do a remote session. I was simply going to tap in to the 9V leads on both the camera/mic and PowerMid/UK receiver and feed them to the IR based power switch contacts. The problem with my original Skype remote control hack was that the battery on the camera/mic would die in about 4 hours. Since, according to the manufacturer, the IR based power switch can go for days on a 9V battery I would have ended up with a long haul remote control spy bot. The only requirement would have been to make sure I parked Roboquad by a second AC based PowerMid so that it could turn the IR switch off when I was done with a session, and back on when you called back on.

But life and the appearance of Rovio have put that hack on the back-burner. :(


GWJax's picture

Thanks for the comment But I'm not sure I understnd what you are trying to do with the mod on the Quad. Is there something I can help you with even though I do not have the Rovio?


roschler's picture


No. I was just lamenting over a Roboquad (not Rovio) mod/hack that I had to abandon because of time constraints. The mod would have made the Roboquad a viable (but kludgy) solution for long term remote viewing.

GWJax's picture

Oh ok, got ya.. Sorry about that!