Digital IR sensor problems

We're building a media-installation with 5X Analog micropone and 5X digital IR sensor on an Arduino board with Flash interfacing. The audio sensors work perfectly with a zero value when there's no sound and about 180 when you talk into them directly.

So far so good but when we hook up the ground for the digital sensors (Infrared) everything starts to go wrong. The IR works but it causes a major disturbance in all the channels both analog and digital.

We tried splitting the ground cables between analog and digital and re-checking every connection but that doesn't seem to be the problem.

Since the digital signal triggers an engine it would be nice if it actually processed the right data. If anybody has some info or a good idea what this problem is about please let us know, time is running short on our deadline.


it's more than likely one of two things: a noisy power supply, or you're overtaxing the power supply.

To try the noisy power supply theory, just put something like a 470Uf, 16V capacitor between the +5 and ground. A .1UF capacitor would also help.. you can put these between +5 and Gnd anywhere you like, preferable as close as possible to the sensors.

To see if you are drawing too much current from the power supply, multiply the current requirements X the number of sensors. For example, 5 sensors x 50Ma = 250ma required. The Arduino running on the USB bus has lots of current available.. something like an amp. On battery power you can draw up to about 400ma.

I'm guessing it's power supply noise....


Thanks for the quick response now we at least know what options there are for further testing :) Although it prolly isn't the power supply, since we're directly getting power through a 9V Adapter with the Arduino on the Ext jumper setting. It could be the noise however, we won't know for a few more hours because we have to wait for the academy to open so we can get an capacitator. could it maybe have something to do with the length of the cables and/or the amount of connection points between the sensor and Arduino the cables are about 50 cm and there are 2 to 3 points of soldering in between? We already connected the sensors a while back without solderings and extra cable and then they were working perfectly.


it sounds like noise... also, what kind of mics are you using? If you are using electret mics, then the current draw from the infrared units will make a little spike in the 5V supply, and this will totally screw up the 5V going to an electret mic supply. This is solved by adding capacitors, as they show a low resistance to sudden changes in voltage: i.e. they get rid of these changes for you, by acting as filters. You can scrounge some from any old broken electronic device. Look up "capacitive reactance" if you want to impress your prof.

While you're at the academy, maybe it's time to track down one of your profs for a power supply lesson :)


You can also use two power supplies. One to power the Arduino and one for the infrared diodes. This would keep those voltage spikes off the Arduino line. If you use some npn driver transistors such as 2n2222 or 3904's or maybe an N chan mosfet as a driver/ switch. You can isolate the power supplies.

I don't have the time right now to draw you a schematic but it's easy electronics if you can find someone with a bit of knowledge.

Write back if you don't get it figured out and I'll post a schematic.