View Full Version : Relay to control 2 outputs
Micah Chetrit
10-06-2011, 13:52
Hey everyone.
I have an off season project to make LED rods and put them on the robot and get them to light up in patterns (I am also a programmer). Being that there are going to be 4 rods, I thought I could save space and money by using only two Spike relays, attaching two Positive wires to it and using a common ground that isn't run through a relay.
If I recall right, this has been used for solenoids (? might be wrong). In my mind it should work, is there any reason it shouldn't?
Secondly, is it legal to control two outputs with one controller? (haven't read rules for a long time, I forgot many of them)
Thanks in advance,
Micah
This is an off-season project, legality is not an issue.
There is no reason why it wouldn't work. In LV at least, the Spike has four output states (Off, Forward, Reverse, and On). Fwd will set one on and the other off, Reverse will set the second one on and the first one off, and On will turn them both on.
Micah Chetrit
10-06-2011, 16:39
the reason legality is an issue is that I am making two sets, one for the current bot, and one for next years bot (using the same code)
Travis Hoffman
10-06-2011, 17:05
the reason legality is an issue is that I am making two sets, one for the current bot, and one for next years bot (using the same code)
See R42. Controlling 2 solenoid or low-current light outputs with one Spike has been legal for many years. As long as you properly send the negative wires back to a black PD board negative terminal (presumed ok to splice the negative leads to fit into a single terminal), you should be fine.
However, what would not be legal is preparing these LED arrays and wire harnesses for use on a 2012 FRC robot - you must wait to perform all such work after kickoff of the 2012 season, during approved robot work times.
Micah Chetrit
10-06-2011, 17:13
Oh, I didn't know about that.
what specifically is forbidden? Can I wire the leds and put them in a tube (therefore just creating a part), but not wire it to a relay? or is making custom parts before season not legal?
Travis Hoffman
10-06-2011, 17:18
Oh, I didn't know about that.
what specifically is forbidden? Can I wire the leds and put them in a tube (therefore just creating a part), but not wire it to a relay? or is making custom parts before season not legal?
The latter case is true. Until the rules change, you cannot fabricate custom parts or construct custom assemblies for your official FRC robot prior to the start of the season. This is one of the core tenets of the FRC program - every team must engineer their robot within the same time window.
Micah Chetrit
10-06-2011, 17:20
Thank you for pointing that out. I guess I only have to make one set this summer then.
Al Skierkiewicz
10-06-2011, 19:10
Micah,
It is also possible that this wiring method would be illegal during next year's game and rules. I would hope that the GDC allows teams to use this method but you never know for sure. As stated the Spike is capable of switching either or both outputs between high and low states. The manual for the Spike explains this.
Hugh Meyer
11-06-2011, 17:27
Micah,
If you connect them to a Jaguar or Victor you could dim them. With different colors that could give you some interesting effects. You would need to put the LEDs in series to be able to tolerate the 12 volts...maybe 6 LEDs and a current limiting resistor. Just an idea...
-Hugh
Just as a note, what Travis said is perfectly true; any design done preseason is not legal for use during competition. However, if the design is modified (i.e. improved or optimized during competition) for the robot, then it is indeed legal.
Although it is worth noting that given that this seems to be more decorative than functional - designing a whole drive train in the offseason is one thing, designing some pretty lights is something else entirely. I wouldn't worry too much about breaking the intent of the "6 weeks" thing.
Steve Warner
12-06-2011, 11:39
I don't have the latest version of the C++ WpiLib source code available to look at right now, but I don't think it allows both relay outputs to be turned on at the same time. Could someone explain why the Relay class was written this way and if it can be changed for the next library release.
I don't have the latest version of the C++ WpiLib source code available to look at right now
Whenever you have access to the web, V20110203rev2259 (http://amhsrobotics.com/wpilib/html/_relay_8cpp_source.html) is available online for browsing.
The only stated differences from V20110203rev2262 are:
1. A NetConsole error in the cRIO that under some circumstances corrupt memory in the cRIO.
2. Fixed an error with the ADXL345 I2C accelerometer.
3. Fixed an error with allocation tracking in the Counter class.
Steve Warner
12-06-2011, 16:02
Thanks Ether. So in Relay::Set there is no way for the kOn case to set both outputs true. I think this is something that could be easily fixed.
To my memory, I believe controlling the 4 states of a Spike involves splicing together two outputs into the Spike input, though I could be wrong.
To my memory, I believe controlling the 4 states of a Spike involves splicing together two outputs into the Spike input, though I could be wrong.
http://content.vexrobotics.com/docs/spike-blue-guide-sep05.pdf
The White input (0/1) controls the M+ output (GND/+12v).
The Red input (0/1) controls the M- output (GND/+12v).
Thus, the Spike can drive a motor forward, reverse, or brake (no coast).
or
Drive two solenoids (or LEDs, etc) independently.
Micah Chetrit
13-06-2011, 14:58
Micah,
If you connect them to a Jaguar or Victor you could dim them. With different colors that could give you some interesting effects. You would need to put the LEDs in series to be able to tolerate the 12 volts...maybe 6 LEDs and a current limiting resistor. Just an idea...
-Hugh
Thanks for the Jag Idea, it sounds like a great idea. I was going to use team color LEDs though, so I am not going to lay too much with colors.
I was planning to put them in parallel however and use a Zenner Diode to regulate the voltage, simply because a 6 led chain isn't very long. I Have not tested the idea yet. I have never used Zenner Diodes before, Any opinion/experience with it? Other ideas?
I was planning to put them in parallel however and use a Zenner Diode to regulate the voltage, simply because a 6 led chain isn't very long.
You can make the chain as long as you like (http://www.chiefdelphi.com/forums/attachment.php?attachmentid=10751&stc=1&d=1307993765).
I have never used Zenner Diodes before, Any opinion/experience with it?
You didn't mention a resistor. Could you post a sketch showing how you plan to use the Zener to regulate the voltage to the LEDs?
Micah Chetrit
13-06-2011, 15:55
You can make the chain as long as you like (http://www.chiefdelphi.com/forums/attachment.php?attachmentid=10751&stc=1&d=1307993765).
I didn't think about it that way before.
I believe I attached a basic drawing of my idea. I might have the directions of the diodes backwards, I don't really do any work in schematics.
Please bear with me, I am still not very experienced.
I believe I attached a basic drawing of my idea.
You've got the Zener shorted across the battery.
PAR_WIG1350
13-06-2011, 16:30
You've got the Zener shorted across the battery.
forget that, he has a conductive loop shorted across the battery (at the far right)!
Wait, I don't see a huge issue with the zener, It is in anti-parallel. X volts go around it and the rest go through it (in a simplified model) . All that is missing is a resistor between everything and the battery to limit current (the wire at the right still needs to go).
forget that, he has a conductive loop shorted across the battery (at the far right)!
Yikes! You're right. I stopped looking when I saw the shorted Zener.
All that is missing is a resistor
That's a pretty big "all". I mentioned the resistor in my earlier post... but whether or not a resistor/Zener circuit even makes sense for this application depends on the current draw for that long chain of LEDs.
Micah, do you understand what we're saying ?
Micah Chetrit
13-06-2011, 16:54
Micah, do you understand what we're saying ?
Yes I do. I am sorry about the mistakes. I really appreciate the input.
Al Skierkiewicz
13-06-2011, 18:21
Micah,
The zener is not really needed unless you are determined to keep the LEDs at a fixed brilliance. Please remember that the battery voltage on the robot easily gets down into the 6-8 volt range during a match. What Ether showed is four LEDS in a string and several string in parallel with a series resistor to limit the current through the diodes. You could choose a three diode string and recalculate the series resistor. The string would stay on if the voltage falls to the 6 volt range. If you think you are up to it, a current source using a FET or transistor might be a better choice in this application.
Micah Chetrit
13-06-2011, 18:46
Excuse my ignorance, but why is a transistor good for this? from my knowledge a transistor is used for controlling outputs based on signals.
Excuse my ignorance, but why is a transistor good for this? from my knowledge a transistor is used for controlling outputs based on signals.
There's a lot to learn, but if you're interested in this stuff you are fortunate that you live in a time when so much information is right at your fingertips, literally.
Just Google the phrase "voltage regulator" and start reading. You will be amazed at what you find.
Al Skierkiewicz
14-06-2011, 07:32
Micah,
The luminous intensity of an LED is a function of the current flowing through it. With a simple current limiting resistor, the intensity will vary with voltage supplied. In a constant current source, the current will remain the same with a varying supply voltage. Don't know if this is important for your application but I thought I would throw it in anyway. One place this was used in equipment I worked on is an audio console. This particular design used several LEDs for signalling which options had been selected. By wiring several LEDs in series and using a current source, the switches merely shorted across the LEDs that were not needed. The current source then kept the current constant and the LEDs were the same intensity whether one, two or all seven were on.
PAR_WIG1350
14-06-2011, 08:11
There's a lot to learn, but if you're interested in this stuff you are fortunate that you live in a time when so much information is right at your fingertips, literally.
Just Google the phrase "voltage regulator" and start reading. You will be amazed at what you find.
78xx series regulators are almost as simple as using zener diodes. They come in handy when you need a 5 volt signal voltage, but your controller can only operate at 6-24 volts, not that this is really an issue that we face often, since the digital sidecar does all the voltage regulation itself.
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