Hall wiper PWM slot car controller

Thread Starter

dlatch

Joined May 15, 2016
85
I have learned enough to build a few of these. I want to improve it with a better IC, higher frequency and gate drivers. Forget the hall wiper, I have gone to a convention wiper pot of my own fabrication so the trigger has feel and the start voltage does not effect the final trigger position. (left side of diagram is the "hall wiper") I don't have a non pdf diagram of the new version handy.

here is a short video of it working.

I just want to improve it as a learning exercise.

People say the LM324 cant drive the SUP90 P fets yet it works at least at 470hz. No heat and the wave form seems pretty square at the gates.

I have an LM339 oscillator with adjustable frequency set up but, I am looking for suggestions on the gate drive.

any and all suggestions are welcome.


PWMcontroller.png
 

dante1

Joined Nov 30, 2010
9
i would like to built this controller but but don't understand all of the symbols.
Could you explain the diagram a little better?
 

Thread Starter

dlatch

Joined May 15, 2016
85
The hall wiper is VERY tedius to make. There is no circuit board. I did point-to-point wiring for the whole thing. And It has been determined that it's not as good, for feel, as a wiper board. (it has, literally, no feel) I have built it using a wiper board and some circuit improvements. I'd recommend doing it that way. It is a reasonable project at that point.

I will post more tomorrow. I just saw this post and it's late here.
 

Thread Starter

dlatch

Joined May 15, 2016
85
The wiper: the resistors (seen in the video between the knobs are all the same R and all in series. Between each one is a tap off to a hall output. (open collector, sinks to ground) The diagram shows the off position. The rectangle on the far left side represents the magnet. It is over two switches (swB, sw0) swB turns on the brake circuit and sw0 grounds point A. (no voltage at main PWM input)

As the magnet moves down, a constant current is pulled to ground through more and more resistors. The current is held constant, and each resistor adds or subtracts the same amount, so the voltage at point A rises and falls linear. Q1 above point A is arranged as a 1mA constant current source. The resistors are 226 so each one induces about .22 volts The 5K VR below point A is R1 in the wiper, it is pulled to ground by sw1 and creates the starting voltage. (as high as 5 volts). The PWM and the big PFET output saturates with about 9 volts at point A.

The reason it's not a great wiper is that the starting voltage effects the total voltage. So more start voltage means the wiper reaches full before the end. With less starting voltage the wiper travels farther to reach full. It's not bad since an easy track with a high start voltage doesn't need a long wiper and you can turn it down for a flat track where you want more wiper resolution. But that and the lack of all feel makes it hard to get used to.

If you can build the wiper, the electronics are pretty simple. As a project it is mostly fabrication. I used a small milling machine to drill the precise and very small holes for the Hall switches. 3 holes per switch and there are 32 hall switches in the wiper.

If you still want to proceed more info on request
 
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