View Full Version : Reset problems

01-24-2008, 07:28 PM
Hi all

I'm working on a diesel engine so this is in part a automotive problem

The propeller resets about 3 out of 10 times, when driving a few relays, (which the preheating and starting of the engine)
I've added filters on long power lines, and taken measures to prevent trouble with induction.

So I believe I've narrowed the problem to sparks when the relays connect/disconnect, which probably gets picked up by the reset line.

Question is, could I put a cap between reset and ground, or would this cause problems? (I'm guessing 100nF should be ok?)
The main reason why I just don't shield the relays or the propeller is space constraints

And a big thanks to Parallax, it's been over 10 years since I had this much silicon fun

Nick Mueller
01-24-2008, 07:54 PM
> The propeller resets about 3 out of 10 times, when driving a few relays, (which the preheating and starting of the engine)

Is the Propeller driving the relays? If so, do you have a fast diode across the relay?

I do have the impression, that the Propeller is a bit picky considering noisy environments.
And a car is *very* noisy (Diesels not as much). Only thing you can do is place a cap near every power-in pin of every chip, have resistors on any in/out, have a diode-L-C combo on the power in.
At least I'll do that with my re-design of the PCB (for the ignition system).

I even observed that values got corruped but the Prop didn't reset. This did not happen on the kitchen-table, but only in the real environment.


Never use force, just go for a bigger hammer!

The DIY Digital-Readout for mills, lathes etc.:
YADRO (http://www.yadro.de)

01-24-2008, 09:35 PM
I have a Prop protoboard in a harsh EMI environment and the first thing I learned was to disconnect the Prop Plug from the protoboard prior to testing... the USB cable seems to act like an antenna and makes the Prop reset if it's attached during an EMI event...

01-25-2008, 12:31 AM
hmm, the diodes are just common 1N4001 rectifiers, might be worth testing a faster type

Following measures have been taken:
IC's have caps right next to the pins,
power in is fully filtered as well, diodes to prevent reverse polarity & L-C filter
Prop plug is disconnected,
all input has resistors to bring a 24v erroneous connection down down to 2mA max,
all external output is driven through a ULN2003 (darlington array)
large caps on the few spots on the power lines where there are power hungry IC.

Which reminds me, I could try using the darlington array's flyback diodes in parallel with the 1N4001's.

Might be that my programming header could be better shielded, sigh, guess there's no quick and dirty solutions, it's time for the trusty scope
The reset line run about 5-7 inches long to a pushbutton=>gnd, I fear this works a little bit to good as an antenna.

Phil Pilgrim (PhiPi)
01-25-2008, 12:50 AM
How you connect your wring is important: Make sure that the ground return on your Darlington driver connects directly to the power supply and not via the ground connections of any of your logic circuitry. When the relay activates, it sends a current pulse to ground, which could raise the Vss level on any connections it encounters on it's way back to the power supply (ground bounce). This may cause the differential between Vdd and Vss to decrease to the point that the Propeller's brownout detector resets the chip.

Also, if your relays are driving inductive loads, those loads can be snubbed with diodes in the same way as the relay coil itself. This will reduce contact arcing and extend the contacts' useful life.

Finally, if you think your reset pin is being activated by noise, try pulling it up with an additional, external resistor of 2.2K or so. This will stiffen the weak pullup interior to the chip itself.


Post Edited (Phil Pilgrim (PhiPi)) : 1/24/2008 5:55:27 PM GMT

01-25-2008, 01:03 AM
Thanks a bunch,

Yes I'm driving inductive loads, and I think you've solved my problem, I'll add fly-backs to snub the inductive loads as well (it seems fitting as the reset only occurs when the relay disconnect, now that I've cut down the length of the reset wire)

Hmm, I noticed a few glitches in the pulses from one of my 555 timers, which seemed to occur at the same time, might be that I have a ground bounce there.
The prop should be good thou, it's relatively close to the powersupply and has separate lines for vdd-vss on both sides of the DIL, with 100nF caps.

Fantastic, 3 answers in one go, I'll need to sort out the ground bounce on the 555 anyway, and snubbing the inductive loads makes sense, and will probably solve the problem.
And if all else fails, I'll add a resistor on the reset.

Post Edited (Håvard) : 1/24/2008 6:10:50 PM GMT

Nick Mueller
01-25-2008, 05:00 AM
The 1N400x series really isn't fast. Use it in 60Hz rectifiers. http://forums.parallax.com/images/smilies/smile.gif
A Schottky-diode is what you want (can't name you one out of my head).

Don't know what currents you have to expect, but you can *try* it with a 1N4148 just as a proof that things get better. Normaly, you should find them in your box stuffed with electronics. But I do *not* recommend using it for real.


Never use force, just go for a bigger hammer!

The DIY Digital-Readout for mills, lathes etc.:
YADRO (http://www.yadro.de)

01-25-2008, 05:45 AM
Nick Mueller said...
(can't name you one out of my head).

Accidentally I can http://forums.parallax.com/images/smilies/smile.gif
They are called UF4001 etc. Fairchild I think..
I sometimes use a 1N5818, but I think it is not rated for some 100 V...