*unofficial* FIRST IR module driver released

[Phil Mack]

Originally Posted by JBotAlan

Let me know if you have any suggestions/concerns/problems/questions and I'll try to address them.

Powering a micro controller with an unregulated supply off of the 12v battery that will be driving motors and firing relays will be unreliable and possibly damaging. The voltage will be unstable, which would make readings unpredictable. Noise in the power supplied to the device can also cause the device to reset or freeze constantly. If the device becomes damaged, it is entirely possible that there would be the same effect as hooking up the digital inputs directly to the battery.

To power this device while attached to the robot, it would be wise to design a power supply. See http://en.wikipedia.org/wiki/Voltage_stabilizer for a starting point. To connect this device to the robot controller, it would be wise to use opto-isolators/optocouplers to protect the devices from each other. See http://en.wikipedia.org/wiki/Opto-isolator for more information.

~Phil

[billbo911]

Originally Posted by Phil Mack

Powering a micro controller with an unregulated supply off of the V battery that will be driving motors and firing relays will be unreliable and possibly damaging.
To power this device while attached to the robot, it would be wise to design a power supply.
~Phil

According to the "The board contains an IR sensor, a CMOS microcontroller, a 5V voltage regulator,...."

No additional power supply should be needed. That is why section 6 states,

"6 Operating Voltage, Output Current
6.1 Operating voltage range
The onboard voltage regulator needs at least 7 volts DC, and can accept more than 15 volts. To avoid
problems, a reasonably clean voltage source is recommended to power this board. Avoid having any noise
glitches on this supply that go below 7 volts DC."

I would agree, running it from the main +12 V battery may be a little risky, but running it from the 7.2Vdc backup adds an additional load to that battery that will need to be accounted for. So, how do you handle this???
As long as the rules will allow it, use a large mAh battery for the backup, say 1500mAh???

[Phil Mack]

Originally Posted by billbo911

The onboard voltage regulator needs at least 7 volts DC, and can accept more than 15 volts. To avoid
problems, a reasonably clean voltage source is recommended to power this board. Avoid having any noise
glitches on this supply that go below 7 volts DC.

You seem to disagree that a better power supply is needed, but then cite exactly why a better power supply is needed, so I'm confused.
If the device is running in and of itself, connected to nothing but a battery like the KOP backup battery, then the voltage supplied by the battery would be sufficiently clean for the simple regulator (that is onboard the device) to power the device.
If the device is being powered by the 12v battery of a complete robot, there are many other noisy loads on it that can easily drop the voltage below 7 volts for however short a time. That is probably enough to cause a problem for the embedded micro controller if it is anything like any other PIC that I've worked with.
So I would probably add another stage of voltage regulation just like the regulator circuit on the device, but with larger capacitors and think that would probably be fine, but I'm not so confident in that idea as to post it as a solution.
~Phil

[Binome]

Well, since the board has a 7805 linear regulator on it, simply throw a large noise filter capacitor on it, and run it off the main battery. The capacitors will keep the voltage at a steadyish 12v, and the 7805 will burn off the rest of the voltage as heat.

[billbo911]

Originally Posted by Phil Mack

You seem to disagree that a better power supply is needed, but then cite exactly why a better power supply is needed, so I'm confused.
If the device is running in and of itself, connected to nothing but a battery like the KOP backup battery, then the voltage supplied by the battery would be sufficiently clean for the simple regulator (that is onboard the device) to power the device.
If the device is being powered by the 12v battery of a complete robot, there are many other noisy loads on it that can easily drop the voltage below 7 volts for however short a time. That is probably enough to cause a problem for the embedded micro controller if it is anything like any other PIC that I've worked with.
So I would probably add another stage of voltage regulation just like the regulator circuit on the device, but with larger capacitors and think that would probably be fine, but I'm not so confident in that idea as to post it as a solution.
~Phil

Your confusion is well founded. I did contradict myself, a bit. I guess what I was trying to say is that the regulator onboard will work fine until the supply voltage dips below ~7vdc, and as you point out, for no matter how short a time. At that point, it is worthless.
Honestly, I don't know if adding a couple caps is legal, but it certainly would provide the filtering needed, assuming they were large enough. So, instead of advising adding more caps, I opted for using a more robust power source. The backup battery will have enough power as long as it has enough capacity. As of last year, a larger backup battery was within the rules, as long as you charged it from the KOP charger.