Pages: 1 [2]   Go Down
Author Topic: Tach circuit causes instability/crashing  (Read 1708 times)
0 Members and 1 Guest are viewing this topic.
Greenville, IL
Offline Offline
Edison Member
*
Karma: 15
Posts: 1330
Warning Novice on board! 0 to 1 chance of errors!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset


  You are on the right track with your scope by using it to see the "noise" that your device is dealing with. When you moved your hand and the noise went away, you were shielding the parts with your hand, effectively grounding out the interference. You might want to look up "shielded cables" to see what they look like.

  Spark plugs are fired at around 35,000 volts +. If you have a mid 90's Chevy pick-up, the spark plugs fire at around 50,000 volts. My point is that spark plugs generate signals that are a lot like lightning storms that mess-up your Television Set or your radio.

   Electronic devices have had to be developed around these problems so that when you are in car and listening to the radio, you do not hear the spark plugs firing over the speakers. I had a 75 Dodge truck with terrible spark noise that would come over the radio. It was like a high pitch buzz that varied with engine speed .

 The solutions are numerous, twisted pair wiring, capacitors, inductors, shortened traces, and shielding to name a few.

 You will have to experiment,
Mark

 
Logged


Offline Offline
Full Member
***
Karma: 0
Posts: 167
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset

Ya, unfortunately I think my scope is causing more problems than it's helping.  I hooked the 2nd LCD display up like I mentioned and got it to a point where one of the screens was "crashed" while the other still functioned fine (for a short time :p) confirming that the displays are my biggest problem at the moment.  With my test leads hooked up to the power pins of the (new) display I can almost guarantee display corruption within several seconds of regular display updates beginning to take place.  With the leads unplugged the system will run for significantly longer before displaying issues (and sometimes not at all)

So I'm taking a step back and going to go get a solid metal project box for this and attempt to bundle the whole thing up and then work backwards from there.  I'm assuming that I should ground the shield to the same "ground" that I'm pulling power from and I should keep the shield grounds off the PCB as much as possible (entirely with a shielded box)

I see lots of talk about RF chokes, but that all seems to be in the Mhz range, where the big ignition pulses are all in 10s to 100s of Hz, and with pulsewidths more like those of a 40khz signal.  I'm thinking about trying RC filters on all the cable lines, switching to proper twisted pair wiring, and/or TVS diodes.

I guess I was really hoping to avoid lots of that because of all the other bike and scooter projects that seemed to get by with minimal suppression and almost no shielding.
Logged

Greenville, IL
Offline Offline
Edison Member
*
Karma: 15
Posts: 1330
Warning Novice on board! 0 to 1 chance of errors!
View Profile
 Bigger Bigger  Smaller Smaller  Reset Reset


I see lots of talk about RF chokes, but that all seems to be in the Mhz range, where the big ignition pulses are all in 10s to 100s of Hz, and with pulsewidths more like those of a 40khz signal.  I'm thinking about trying RC filters on all the cable lines, switching to proper twisted pair wiring, and/or TVS diodes.


 Ignition pulse occur at 10s to 100s of Hz but, the signals produced by them are transients that cover many frequencies. If you could imagine a signal "blast" kinda of like hitting 30 piano keys all at once. It would sound like one bad note but, the note contains many frequencies both high and low Hz.


Mark
Logged


Pages: 1 [2]   Go Up
Jump to: