Powering the IR detector from +5V instead of 7+ V.

[PhilBot]

Considering that the IR detector board is an input sensor (not an actuator) and it only draws 20ma at most, is there any reason why it can't be modified to run on +5V supplied by the Digital Input connector.

It just seems that this would make it much easier to hookup... getting power and providing signals with just two PWM cables (one conventional and one connected sidways on the DIO pins).

It would require modifying the board a tiny bit (by taking the somewhat suspect regulator out of the circuit and feeding the +5V directly to the output trace of the removed regulator), but this does not appear to violate any rules. As is is, some people seem to be replacing the regulator with a more robust one.

Have I missed anything that would prohibit this?

Phil.

[Dad1279]

For testing, after I blew the onboard regulator, I wired it directly to use the 5v from the robot controller and it works fine. However, per <R55> & Q&A Forum:

Question 3: The IR receiver circuit must be protected by a 20-amp circuit breaker (see Rule <R55>). .......

http://forums.usfirst.org/showthread.php?t=8539

[Dave Flowerday]

Originally Posted by Dad1279

For testing, after I blew the onboard regulator, I wired it directly to use the 5v from the robot controller and it works fine. However, per <R55> & Q&A Forum:

Question 3: The IR receiver circuit must be protected by a 20-amp circuit breaker (see Rule <R55>). .......

http://forums.usfirst.org/showthread.php?t=8539

I'm not sure how to interpret that. If you use the +5v from the RC, the IR receiver IS protected by a 20-amp circuit breaker... (since the RC is powered through a 20-amp breaker).

In the past they specifically have allowed sensors and custom circuits to be powered by the RC's 5v rail. I don't know why that would be any different this year?

[Dad1279]

Dave, I would agree with that logic, and was surprised by the Q&A answer.

However <R55> reads as follows:
.....
• The Robot Controller power feed must be protected with a 20A circuit breaker. No other electrical load can be connected to this breaker.
......
• Power feeds to custom circuits and additional electronics must be protected with a 20A circuit breaker.
......

So I intend to build a 'custom circuit' consisting of a 5v regulator, on a separate circuit. This will power the IR receiver, etc.

I think it is a mistake to power the IR circuit directly from a 20A circuit anyway. (A potential of 20A going through the ribbon cable) The 3 terminal external regulator will also limit the current.

[Dave Flowerday]

Originally Posted by Dad1279

However <R55> reads as follows:
.....
• The Robot Controller power feed must be protected with a 20A circuit breaker. No other electrical load can be connected to this breaker.
......
• Power feeds to custom circuits and additional electronics must be protected with a 20A circuit breaker.
......

In past years, R55 has been interpreted to mean that *if* you feed a custom circuit 12v, then it must be from a 20A breaker. However, custom circuits that were powered from the RC's 5v line were specifically allowed (and I asked a Q&A to make sure):
http://forums.usfirst.org/showthread.php?t=1518

Now, there's the standard catch about "last year is not this year", but when the rule in question does not change at all from 2007 to 2008, and this is how it was interpreted in 2007, then I don't see why anything would be different this year.

[PhilBot]

For example...

If you were using the CMU cam, noone would expect you to run a 12V line through a breaker, and then a voltage regulator (to reduce it to 7V or 5V) and then to the CMU cam...

You'd just plug it directly into a PWM port for power.

It is an input after all.

[Al Skierkiewicz]

Dave and Phil,
Someone needs to ask this on the Q&A as the supplied IR board has provisions for running from a 5 volt supply by eliminating the regulator. There is a note to that effect on the FIRST supplied schematic. I fully agree that a 20 amp breaker does not match the elctrical code for wiring used elsewhere on the robot.

[PhilBot]

Originally Posted by Al Skierkiewicz

Dave and Phil,
Someone needs to ask this on the Q&A as the supplied IR board has provisions for running from a 5 volt supply by eliminating the regulator. There is a note to that effect on the FIRST supplied schematic. I fully agree that a 20 amp breaker does not match the elctrical code for wiring used elsewhere on the robot.

Good idea... I'll see what I can do. Good tip about the added comment on the FIRST schematic. I didn't see that on the original one.