Comment by Damon Pipenberg on July 3, 2009 at 10:43am

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.

Admin Comment by Thomas J Coyle III on July 3, 2009 at 10:50am

bGatti,

Since the schematic (ArduPilot-V15) for the Ardupilot on the Sparkfun website does not include the ATTiny nor the Multiplexer, I going to assume that all of the ICs on the Ardupilot board are powered by the receiver throught the servo inputs. The only time that the onboard regulator is used is when the board is powered through the battery input and the onboard jumper is moved from the servo to the battery position.

Most RC manufactures are explicit about powering the receiver with only 4 rechargeable batteries and not 4 AA cells. The NMHi batteries ususally charge up to ~1.3 v each resulting in a 4 pack voltage of around ~5.2 v which is well within spec. If the receiver is powered by the 4 pack and the Ardupilot is powered by the receiver, there should be no voltage differential between the receiver and the Ardupilot. If the board is powered by the onboard regulator from a separate battery and the receiver voltage is greater than say 5.5 v, which is possible with present day receivers, there definitely could be an issue.

Just a thought.

Regards,
TCIII

Comment by bGatti on July 3, 2009 at 11:17am

@Damon,
What's the humidity like where you live?
- I take you're point on the battery set-up.
Essentially you're ruling out the idea of the receiver being powered up and connected to the AP without the ap also being powered up. That would take the 12x overvoltage out of the equation.

I would take a second look at how you're doing that and confirm that there isn't any combination of connections which pushes a receiver signal at the AP without it being powered.

Next we're ack to the issue of the regulator pulling down the VDD on the mux. This is a small overvoltage, but might as well rule that out. Explaining everything with ESD, is about like explaining everything with GOD in my book, neither one of them is a persuasive answer.

Comment by bGatti on July 3, 2009 at 11:18am

the test is easy.
disconnect the receiver from the AP,
measure the AC voltage of the servo signals. reconnect the AP and remeasure the AC of the servo signals. The change is being absorbed by the MUX.
Ben

Comment by Damon Pipenberg on July 3, 2009 at 11:46am

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.

Comment by bGatti on July 3, 2009 at 12:01pm

@Damon,
Now we're getting closer.
You're elevons don't have a ground wire?, They are floating until you plug something else in. If the next thing has a ground first plug, or it's put in sideways etc, you can definitely push 12x into the board.
Ben

Developer Comment by Ryan Beall on July 3, 2009 at 2:35pm

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!

Comment by Michel Lubbers on August 15, 2009 at 4:49am

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.

Comment

• ‹ Previous
• 1
• 2
• 3
• Next ›
• Page