Simulating a Hall Effect Trigger with the Prop
DavidGreg
Posts: 38
Hello all-
I have a nice little spark ignition box that is designed to be triggered from a hall effect sensor. I use it to just generate sparks continuously at about 40 Hz. I've been using an old tektronix function generator to "simulate" the hall effect sensor by connecting it to the trigger and ground pins on the hall sensor connector. I would like to use a propeller to directly serve the same purpose as the function generator.
I've tried several different schemes with no luck. In all of them I've grounded the ground pin of the connector and moved the trigger to various places such as:
1) Connected to a prop pin pulled up to 3.3V
2) Connected to a prop pin pulled down to ground
3) Connected to a prop pin with no resistors
4) Connected to the drain on a MOSFET with a pullup on the drain, source connected to ground, and gate connected to a prop pin.
It was my understanding that most ignitions with hall sensors trigger when the signal is pulled to ground and that the high voltage doesn't much matter. Is that correct?
I have a nice little spark ignition box that is designed to be triggered from a hall effect sensor. I use it to just generate sparks continuously at about 40 Hz. I've been using an old tektronix function generator to "simulate" the hall effect sensor by connecting it to the trigger and ground pins on the hall sensor connector. I would like to use a propeller to directly serve the same purpose as the function generator.
I've tried several different schemes with no luck. In all of them I've grounded the ground pin of the connector and moved the trigger to various places such as:
1) Connected to a prop pin pulled up to 3.3V
2) Connected to a prop pin pulled down to ground
3) Connected to a prop pin with no resistors
4) Connected to the drain on a MOSFET with a pullup on the drain, source connected to ground, and gate connected to a prop pin.
It was my understanding that most ignitions with hall sensors trigger when the signal is pulled to ground and that the high voltage doesn't much matter. Is that correct?
Comments
1) There's probably a pullup internal to the box. If the resistor value is too low and the voltage is too high, it can damage the Prop's I/O pin circuitry.
2) If the logic high voltage is higher than 3.3V, the box may see the Propeller's 3.0V logic high and think it's the same as a logic low.
3) Choice #4 is the most likely to work
Any information available on the output signal characteristics of the Tektronix function generator which seems to work?
The Tektronix is a FG504 like this one: http://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_500/FG504.htm
The output is labeled "from 50 ohm". I have the attenuation set at 0 db. It triggers over almost the entire range of the P-P knob except for just a little range at the beginning. Unfortunately, it looks like my knob was tweaked at some point because the range of motion clearly doesn't match the label. I have a scope, but only one BNC probe, so I'm not sure if I can scope the wave form and see at what voltage it stops triggering.
I have the mosfet drain pulled up to the Protoboard's VDD via a 1k resistor. I'm thinking I will try pulling up to the power supply input voltage tonight.
Thanks!
David
So, I ended up connecting the trigger directly to a prop pin, with an 80 ohm resistor in series. It seemed to do fine with no resistors at all, but it works fine with the 80 and that should prevent any thing serious from happening to my board if the ignition trigger circuit should short.
Thanks for the help!
Post Edited (DavidGreg) : 10/3/2009 1:13:15 AM GMT