Flawed IR Design Confirmed

[keen101]

OK, after frying the 5V regulator on our IR board twice, I think I can safely say that the IR board has a flawed design. Although, I know how I fried it the second time. It was because I accidentally reversed the polarity of the input voltage. Apparently the 5V regulators do not take reversed voltage very well.

If FIRST decides to use such boards in the future, I would REALLY recommend that they design it with a diode. That way the diode would restrict the current to only go one way.

I have also fixed our board twice. This time, I even had the exact L805 laying around on an old board of something else.

Well, that's all the info I have. I hope this helps clear some things up.

[Phil Mack]

While the device may not be robustly designed, the user neglecting to properly check connections before applying power is hardly a design flaw. All of engineering is about trade offs, and the designers of this board traded simplicity of design, lower production cost, and the ability to accept a wider input voltage for a need of greater diligence on the part of the user.

In any case take this as a lesson to check your work... improperly wiring the IR board may cost you a dollar and a few minutes, but mproperly wiring the RC may cost you $450 and your team's capacity to develop software for this year's competition.

~Phil

[TimCraig]

Originally Posted by keen101

OK, after frying the 5V regulator on our IR board twice, I think I can safely say that the IR board has a flawed design. Although, I know how I fried it the second time. It was because I accidentally reversed the polarity of the input voltage.

So you connect the board with the polarity wrong and they have a flawed design? I'd say it was pilot error.

Originally Posted by keen101

If FIRST decides to use such boards in the future, I would REALLY recommend that they design it with a diode. That way the diode would restrict the voltage to only go one way.

Diodes restrict current flow to one direction, not voltage.

[keen101]

Did i say voltage? oops. I meant current.


...And yes, I think it is a flawed design.


I don't mind replacing 5V regulators. It helps my troubleshooting skills.

..and yes, it is my fault for connecting it wrong, but a better design would help.

[Drwurm]

Thanks for the warning, I'll be sure to tell our programmers about the potential problem.

I definitely agree with you that any reverse voltage sensitive component should be built with a diode too. It's not like it requires much extra engineering.

[Al Skierkiewicz]

The diode/current statement was correct. You are asking that a diode be placed at the voltage input terminals such that a reversal would cause the diode to be reverse biased and no current would flow. The downside of this kind of design is that the diode drops 0.6 volts when forward biased. In a robot when the drive system demands a lot of current, the battery voltage does fall and that extra 0.6 volts may make the difference between working and not working.

[keen101]

Originally Posted by Al Skierkiewicz

The diode/current statement was correct. You are asking that a diode be placed at the voltage input terminals such that a reversal would cause the diode to be reverse biased and no current would flow. The downside of this kind of design is that the diode drops 0.6 volts when forward biased. In a robot when the drive system demands a lot of current, the battery voltage does fall and that extra 0.6 volts may make the difference between working and not working.

That is definitely a possibility. But, as long as you keep that in mind when designing your robot, then I don't think it would be much of a problem.

[Grovestand]

so replacing the 5v regulator will fix it if we accidently reversed polarity? I mean, we realized we only reversed it for a split second and now it doesnt work during our first connection....didnt think that a connection of under 2 seconds would break it, but whatever

[pheadxdll]

Originally Posted by Grovestand

so replacing the 5v regulator will fix it if we accidently reversed polarity? I mean, we realized we only reversed it for a split second and now it doesnt work during our first connection....didnt think that a connection of under 2 seconds would break it, but whatever

Electricity can travel pretty fast in 2 sec ;p. Before you go out and buy another board, try replacing the regulator. It should fix it. If it doesn't, then you'll have to buy another one. :/

Our team has only hooked the IR board once and thankfully we got the polarity right.

[jerry w]

the fragile nature of this board is very disappointing. i do believe that it was not intended for robot mounting. but, it was adapted to the task. it makes no sense to run the board on 12 volts when the 5 volt line is readily available on the RC.

jerry w

[d25inferno]

ummmm...i know its an odd time to ask this but how do u hook the board to a powersource we split the black and white wire and directly connected it to a 6 pack AA battery set......the wires got extremely hot and the tip started to burn

please help on this issue

[Pat Fairbank]

Originally Posted by d25inferno

ummmm...i know its an odd time to ask this but how do u hook the board to a powersource we split the black and white wire and directly connected it to a 6 pack AA battery set......the wires got extremely hot and the tip started to burn

That would be because the black and white wires (the first two) go to the same place on the board - the voltage input. You were essentially shorting out your batteries. Try connecting the black wire to the positive battery terminal and the grey one (the third wire) to the negative battery terminal.

[PhilBot]

Originally Posted by keen101

...And yes, I think it is a flawed design.
..and yes, it is my fault for connecting it wrong, but a better design would help.

Seriously but.... When you accidentally connect the 12V to one of the logic output pins, where will you put the diode to correct that design flaw

Phil.

[keen101]

I have finally wired it up to a PWM cable. There should be no need for a diode now, since the PWM cable cannot provide reverse voltage. But, i suppose if i was really paranoid I could splice the red wire on it and add a diode there.

[The Lucas]

Originally Posted by keen101

I have finally wired it up to a PWM cable. There should be no need for a diode now, since the PWM cable cannot provide reverse voltage. But, i suppose if i was really paranoid I could splice the red wire on it and add a diode there.

If you are using the PWM cable to connect it to the RC's PWM Output (which draws power from the 7.2V backup battery), the 0.6V voltage drop of the diode would likely cause the voltage to drop below the required 7V (or only work for a short time since fully charged backups can be up to 8.4V). Compatibility with the backup battery might be the reason there is no diode already on the board.

P.S. you can get reverse voltage from a PWM cable if you flip the connector and plug in only 2 pins (red to black). I've seen them plugged in that way on a crowded RC.