Wondering if anyone might have experienced a problem that I'm having. My ArduPilot has been working fine, but yesterday, the servo outputs suddenly quit working. After doing some troubleshooting, I think I've narrowed the problem down the the multiplexer (74ACT157). It gets power, and gets a proper signal from the failsafe, and I found a 50 Hz signal on the inputs. However, the outputs are always low, at 0V.I've been using a 4-cell, 4.8V receiver battery to power my setup. When fully charged, it gets up to 5.3V, which should be safe for the multiplexer. Maybe I shorted out one of the outputs, or zapped it with static? Anyone else had a similar problem?
I also fried the 74ACT157, I replaced it with a 74HCT157 (cmos), now my servo's run directly to the corner. What could be wrong? Perhaps the gate stays down or something like that. I try a 10k pullup resistor but no positive result.
I have never fried anything with ESD and I have taken very little effort in my 5 years of tinkering. I would suspect bGatti's claims and serch out any scenario where you put the MUX out of spec that or it simply went bad. Really a 50cent part went bad.... Dang it gonna break the bank. Enjoy the search!
Ben,
Thanks for the tip. I'll try that out when I receive my replacement AP. I tested the broken one, and the voltages are exactly the same, but that doesn't mean much since it is already fried.
The humidity varies a lot here, but during summer its probably humid more often than not. So static is not usually a problem, but the foam on this plane does seem to generate some static. I know, I don't really have an quantifiable evidence that points to static.
The only situation I can think of where the AP could receive a signal when not powered is from the elevon signals. However, in that case, ONLY the signals would have been connected, and the ground and VCC of the
AP would be floating. If those inputs were at different levels, maybe this could cause a problem, but I'm not familiar enough with CMOS logic to know.
I should clarify how I have my ArduPilot setup. I am not powering the AP separately. I have a 3-pin female to female lead to connect the receiver to the CTRL input on the AP. This connects the power buses on the receiver and AP. I then use jumpers to connect the 2 servo signals for the elevons. I connect my 4.8 V receiver battery to either an extra servo input on the AP, or to the revceiver. Either way accomplishes the same thing, as the power buses are connected together. So, because of how I connected my system together, I do not believe that I violated the specs on the MUX. I guess that it could be an issue when the board the battery is being connected or disconnected, but it seems unlikely to be the problem, as I have been working with it like this for several weeks.
The voltage from my battery varies from maybe 4.7 to 5.3 volts. This is within the spec of all the devices on the AP. I am assuming that the servo signals from the receiver are not boosted above the supply voltage to the receiver. My setup is almost identical to that of someone using a BEC, with the exception that my battery is not regulated to 5 V. A typical BEC can source 2 amps, while my battery can probably source more if it is shorted. However, 2 amps is way more current than it would take to fry the MUX, so the current limit from the BEC is not protecting the MUX.
I believe that the MUX was damaged due to ESD. I have not be very careful about ESD protection, and have been playing with the board on the bench for several weeks, and it has worked just fine. However, I recently installed the board in a Zagi (foam) and brought it outside for some ground testing, after which the multiplexer was fried. The combination of a foam plane and wind outside leads me to believe that ESD was probably the cause.
If you are using what Chris Anderson calls the typical setup: Battery -> ESC/BEC -> Receiver -> ArduPilot, I believe that you should not have to worry about over voltage problems with the MUX. You certainly should take care not to short the outputs, as that could easily damage the MUX.
This seems probable that many people would have this issue unless they all power the MUX from the servo lines? That, or they are all getting lucky and turning their Ardu board on first.....
Jordi,
The board I have has a 74ACT157 chip on it, which I believe is CMOS. Your schematic however, lists a 74LS, and that is also the part listed in the build instructions.
I"m pretty sure that all of the channels of the mux are dead.
Anyways, it is not a big deal, I ordered a couple more of the ArduPilot boards and I'll replace the broken one with a 74LS version when I have a chance.
Also, I'm sorting out the voltage regulator situation, in case that was the problem
The Mux is not a CMOS is normal TTL. I heard of someone else that also burned only one channel (ch1), and what he did is used the channel 4, by only soldering a jumper wire from ch1 to ch4 and connect the rudder on port 4. But if you are sure you didn't burn it, you must request a refund from SparkFun.
The ardupilot power regulator is good to powering the ucontrollers only, but you must use a separated battery for servos.
Oh. Well, that was a mistake. You ran power through the board without a power regulator. You almost certainly fried it. Power regulator's don't just limit voltage, they limit current, too. The manual is pretty clear on the need to switch the jumper. I think you need a new board.
No, I did not. I decided that since the battery voltage would be under the max voltage of the devices, it would be ok. I'd expect this to cause other problems, such as drifting A/D values as the battery voltage decreased, but I doubt it would fry the multiplexer.
Comments
Thanks for the tip. I'll try that out when I receive my replacement AP. I tested the broken one, and the voltages are exactly the same, but that doesn't mean much since it is already fried.
The humidity varies a lot here, but during summer its probably humid more often than not. So static is not usually a problem, but the foam on this plane does seem to generate some static. I know, I don't really have an quantifiable evidence that points to static.
The only situation I can think of where the AP could receive a signal when not powered is from the elevon signals. However, in that case, ONLY the signals would have been connected, and the ground and VCC of the
AP would be floating. If those inputs were at different levels, maybe this could cause a problem, but I'm not familiar enough with CMOS logic to know.
The voltage from my battery varies from maybe 4.7 to 5.3 volts. This is within the spec of all the devices on the AP. I am assuming that the servo signals from the receiver are not boosted above the supply voltage to the receiver. My setup is almost identical to that of someone using a BEC, with the exception that my battery is not regulated to 5 V. A typical BEC can source 2 amps, while my battery can probably source more if it is shorted. However, 2 amps is way more current than it would take to fry the MUX, so the current limit from the BEC is not protecting the MUX.
I believe that the MUX was damaged due to ESD. I have not be very careful about ESD protection, and have been playing with the board on the bench for several weeks, and it has worked just fine. However, I recently installed the board in a Zagi (foam) and brought it outside for some ground testing, after which the multiplexer was fried. The combination of a foam plane and wind outside leads me to believe that ESD was probably the cause.
If you are using what Chris Anderson calls the typical setup: Battery -> ESC/BEC -> Receiver -> ArduPilot, I believe that you should not have to worry about over voltage problems with the MUX. You certainly should take care not to short the outputs, as that could easily damage the MUX.
The board I have has a 74ACT157 chip on it, which I believe is CMOS. Your schematic however, lists a 74LS, and that is also the part listed in the build instructions.
I"m pretty sure that all of the channels of the mux are dead.
Anyways, it is not a big deal, I ordered a couple more of the ArduPilot boards and I'll replace the broken one with a 74LS version when I have a chance.
Also, I'm sorting out the voltage regulator situation, in case that was the problem
Thanks all for your help.
The Mux is not a CMOS is normal TTL. I heard of someone else that also burned only one channel (ch1), and what he did is used the channel 4, by only soldering a jumper wire from ch1 to ch4 and connect the rudder on port 4. But if you are sure you didn't burn it, you must request a refund from SparkFun.
The ardupilot power regulator is good to powering the ucontrollers only, but you must use a separated battery for servos.
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