Solved: Please Help (Fried Pins) I think i am slowly killing my STE

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Solved: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Sun Aug 27, 2017 10:10 pm

Hello Guys

I have been trying to use my STe to act as a timing system for a slot car track.
I wrote the software and using simple switches on the Enhanced Joystick Port it was working fine.

However once i connected it to the track and began running the cars it worked for a while and then stopped working.
The result of this is.. i believe.. now 3 fried pins on myEnhanced Joystick Port A.
The evidence of this is that the triggering worked for a while and then the triggering became continuous... that is th Voltage difference from pin to ground was no longer about 4.95v but now about 1-1.5V

I tried two circuits and both failed... killing pins.

Circuit 1 uses a 150ohm resistor between the sensor and the +'ve pin.
This was completely reliable for about 50 laps and then killed the pin
Image

Circuit 2 uses a 150ohm resistor between the ground rail and pin 9.
This worked for about 5 laps and killed the pin almost immediately.
Image

I wonder

1. Is my resistor insufficient?
2. Should i be protecting my sensor with a diode?
3. Is there something else. There is no reason for the car to generate anything as the same pickup braid connects the sensor to the ground rail to make the timing connection
Image

Can anybody help?

I have another question regarding the analogue pins but this is my main concern.
I only need 4 pins for my circut but i dont want to kill any more if i can help it.

Can anyone help me protect my STE from my ignorance?
Last edited by AtariOwl on Sat Nov 18, 2017 1:28 pm, edited 1 time in total.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby iceman » Mon Aug 28, 2017 2:58 am

Can you use opto-isolators or relays?
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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Mon Aug 28, 2017 7:08 am

Unfortunately

No i cant use optical.

Relays might be possible i suppose or true dead strip. I had been trying to be clever though and avoid actual dead strips and instead use a split strip.


This brings me to the next problem though.
I had been intending to read throttle position from each lane using the analogue pins to track 'fuel usage'.

Code: Select all

+'ve Rail----------------------------------
                     |
                     1M
                     |
                     ----------------------------------------- Pin 5 or 15
                     |
                     |
                     220k
                     |
                     |
-#ve Rail----------------------------------- Pin 9     


This is likely to kill the pins as well though isn't it? Especially unless i protect them some way.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby Dal » Mon Aug 28, 2017 7:13 am

If you can find a RoboKit for sale, you'd have a very usable solution. And writing the software for that, would be simple too.
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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Mon Aug 28, 2017 7:47 am

I'm not familiar with that.
I suppose finding and cost are likely to be... difficult.


Damn i wish this was just as easy as the simple switch tests.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby joska » Mon Aug 28, 2017 7:55 am

Suggestion: Hook the track up to an Arduino (or clone), and connect the Arduino to the STE's serial port.
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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby Smonson » Mon Aug 28, 2017 9:23 am

Can you give some detail about these sensors? Are they just switches, connecting the 22v rail? If so, you're going to give your joystick port 150mA of current, which is huuuuuuuge.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Mon Aug 28, 2017 10:20 am

Its not really a sesor at all

There is a copper tape lane whic is connected as shown in the circuit diagrams to Pin9 on the EHJ port

Then next to this there is some copper wire which is connected via a 150 or 180ohm resistor to one of the other pins of the EHJ Port

When the copper braid of the car brushes over these two it makes a connection thereby effectively closing a switch


I am thinking of trying to make a voltage or reverse voltage protection circuit across the pins but i really dont know what it is that is killing the pins.

I can't see any obvious readon for it.
There should be no extra source of voltage in teh circyit. Theres no back voltage from the car motor. Theres no obvious reason for it to happen.


I've been considering trying to protect it with a diode but i dont know what i need to do in order to achieve that.


The connection is just as in the circuit


Code: Select all

Pin 9 --------------------Copper tape (Braid makes connection) Copper wire ------------------ 150 Ohm----------------- Pin (one of 1,2,3,4,11,12,13,14)
                                          |
                                          Ground
                                         


There is another rail running parallel to the ground rail, but there should not be any voltage getting to the ground.
I suppose some kind of voltage protection would help but i'm lost now. I cant see any reason for the pins to die.

I assume that is what is happening as after a while they no longer show 5V but insteasd about 1V i sassume SOMETHING is damaged but i dont know what.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby czietz » Mon Aug 28, 2017 10:24 am

One thing to check for -- since you're not using galvanic isolation with e.g. optocouplers or relays -- is ground potential differences. Do you measure a voltage between your car track's ground and the STE's ground? In circuit 2, do you measure a voltage across the 150 ohms resistor, indicating that a significant current flows between the two "grounds"?

Then, particularly if the cable between sensor and STE is long, each time the connection is broken, there is a voltage spike due to the inductance of the cable. While the series resistor in circuit 1 should help protect against it, it possibly is not enough. Use fast diodes clamping to Vcc and GND at the STE's input. There are double diodes specially made for input protection.

The good news is that you most likely just fried the 74LS244 input buffer which is comparatively easy to replace.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Mon Aug 28, 2017 11:03 am

HI

THIS is something i have been worrying about. Ground potential difference, because if i do NOT run the track i just roll the car overthe sensor. Then i get no problem. It is ONLY when the track is live.

1. I have not checked for a difference between slot car ground and STE ground.
2. I tried the 150ohm resistor between live pin and wire and between STE ground and slot car ground... the second arrangement with the 150ohm between STE ground and slot car ground killed the pins much faster.

The cable is perhaps 60cm long

It is very possible that there is current flowing between the two grounds. I think this is most likely the cause.
If its IS? What can i do about it?

Now i must admit my understanding of diodes is limited.
Can you help me understand how i would use the diodes to clamp to Vcc and GND? What ones should i be looking at?


This is VERY helpful... thank you :)

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Mon Aug 28, 2017 12:01 pm

So i connected my DVM across the a 150ohm connected between GNDs

some tiny flickers about 30mV but othyerwise a constant 0V. I suppose that would suggest that the teo GNDs are essentially the same.

I will watch it for a longer period of time to see if there are any fluctuations.
I'm guessing diode protection is what i need.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Mon Aug 28, 2017 1:46 pm

Smonson wrote:Can you give some detail about these sensors? Are they just switches, connecting the 22v rail? If so, you're going to give your joystick port 150mA of current, which is huuuuuuuge.



They absolutely do NOT contact the 22v rail. THat is enrirely separate.
The switch is essentially the braid of the car connecting a wire attached to the joystick pin to the GND rail of the slot which is also connected to the source GND


In circuit 2 i monitored the Voltage across the 150ohm resistor between Track GND and STE GND but i did not observe an difference.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Mon Aug 28, 2017 1:51 pm

I had intended to monitor the throttle position using a circuit like this
Image

Whereby the 10k and 2k2 resistirs reduce it to a level that wont burn up the EJP

The timing sensors do no touch the 22V rail, nor do they span the motor. The connection is made by a single braid from the car in order to prevent any voltage generated from the motor feeding back.

However i still have problems.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Mon Aug 28, 2017 10:55 pm

OK

So i'm thinking if i put some rectifier diodes in the circuit it should at least protect against the wrong polarity

Image

Though this probabloy wont protect the ADC connection so i probably need to have a zener diode i'm guessing at 4.7 or 5.1V in parallel
Image

Is there any way to protect for over voltage on the sensors?

Image

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby mlynn1974 » Mon Aug 28, 2017 11:28 pm

Sorry if my points are too simple but if your pins are being fried then the voltage or ampage must be too high feeding back to the port. This presents an immediate fire risk. How did you fix the STE to continue testing? Did you put a multimeter on the affected pins to monitor the voltage and ampage?

Why is the rail as high as 22V? I take it this power is supplied by a mains operated transformer and not a battery?

An electrician would advise on the correct design of this circuit. I think the diodes and high value resistors are correct to protect the ST, but the Enhanced Joystick ports is still basically for connecting TTL devices and potentiometers. It should never come into contact with high voltage circuits.
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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Tue Aug 29, 2017 7:33 am

Not too simple. Any feedback is helpful.

I have not been monitoring ampage that is a very good point. I have been using a DVM to monitor V.

I havenot as yet connected anything to the 22V rail. I have increased the resistance of the parts i intend to connect to it, but as yet the only connections made have been to the GND and tyhe sensor wire.


The 22V is indeed from a mains transformer.
My new resistances are
Image

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby dml » Tue Aug 29, 2017 8:14 am

Sorry if you explained this already but...

Theres no back voltage from the car motor.


How do you know that's the case? By measurement or some other reason?

Electric motors will produce high voltage noise. This won't show on a normal meter - you'd need an oscilloscope. It is known to destroy semiconductors so protection is needed. Measuring the ground difference and then the noise on the 22v rail using a scope might tell you something.

While it is likely the cars do have protection near the motor, it seems not clear if there is enough to connect the rails to TTL inputs.


Some things to look at:

- reverse protection diode (ultrafast type) and sometimes ceramic capacitor across motor
- 5v zeners across any semiconductor gates (i.e. computer inputs)
- rectify signals with fast diodes
- chokes on signal lines and/or motor wires

Isolation is a good idea even if the ground potential difference averages zero - it can still change briefly depending on the resistance of the track, where the cars are, what the motors are doing, where the common ground point is relative to the sensors and other things.

If the signal you are generating is a pulse you can isolate through a small transformer instead. This also helps clean up some of the higher frequency stuff. You then just have to rectify and clamping the pulse.

Anyway you don't need all of these things at once but you do need to be aware of these spikes and brief changes in ground potential and guard against the things you are unable to measure effectively.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Tue Aug 29, 2017 8:40 am

HI

OK i assume there is no back voltage across the motor because my connection does not span the motor. My sensor ONLY connects one braid it does not span the motor so whatever is happening on teh motor one would hope would not affect the sensor wires or ground rail.

There is a capacitor on the motors i will try to check what it is, but by not connecting to the *'ve rail yet or spanning the motor i was thinking that potentials across the motor were irrelevent.

- reverse protection diode (ultrafast type) and sometimes ceramic capacitor across motor
- 5v zeners across any semiconductor gates (i.e. computer inputs)
- rectify signals with fast diodes
- chokes on signal lines and/or motor wires


1. There are capacitors across the motor i will check what they are
There is no diode on the motors - should i do this?

2. I have added rectifier diodes to the sensor gates. Is this incorrect? How would i use Zeners in this case? I don't understand what i would do with the reverse fail case.
I have added a 5V zener to protect the ADC gate .

3. I have added Rectifiers to the gates
Should i add a rectifier to the GND my guess is not?

4 I dont understand about the choke?

The diodes already substantially increase the resistance on the gates which is pleasing. Should i increase further?

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby dml » Tue Aug 29, 2017 9:07 am

AtariOwl wrote:HI
There is a capacitor on the motors i will try to check what it is, but by not connecting to the *'ve rail yet or spanning the motor i was thinking that potentials across the motor were irrelevent.


While that does seem to make sense - it is unfortunately not the case. The whole thing is one big resistor/capacitor network. There are no perfect wires or connections. This becomes increasingly true as frequency and voltage are increased (both present in back-EMF!).

I'm not saying this is what is killing your joystick port - there is no way of being sure without measuring and/or guarding against it properly. However noise from the motor is certainly able to do that - even if you don't span the motor terminals.

AtariOwl wrote:1. There are capacitors across the motor i will check what they are
There is no diode on the motors - should i do this?


The capacitor is there to dampen the HF noise. It won't prevent reverse polarity but does help with the spikes. You'll get different kinds of spikes when the motor is running vs starting/stopping. I'd add a fast protection diode across the motor+cap which catches any voltage reversal.

AtariOwl wrote:2. I have added rectifier diodes to the sensor gates. Is this incorrect? How would i use Zeners in this case? I don't understand what i would do with the reverse fail case.
I have added a 5V zener to protect the ADC gate .


TBH I would instead use a zener between the signal pin and signal ground, and add a choke to each signal wire. If the signal reverses, the zener will conduct. If the signal passes zener voltage, it will again conduct. The signal is then clamped.

However I'd also isolate if at all possible. Sudden ground potential changes are just as bad if not worse. Also the zeners can handle only a limited current before they fail. EMF shouldn't generate much current but ground potential differences certainly can.

AtariOwl wrote:Should i add a rectifier to the GND my guess is not?


No - either isolate fully, or ensure GND is common with minimum resistance between them. I'd prefer isolation though.

AtariOwl wrote:4 I dont understand about the choke?


A choke is just a coil with enough inductance to flatten/soak a high frequency signal. All coils have a frequency component and respond to that frequency, but impede e.g. higher frequencies. So putting a coil in series with a signal will.. err... 'anti alias' or soften the signal ;) it's a cheap way to get rid of EMF and spikes.

(The spikes are still there but the voltage has been converted into another form - current, or spread over time. However you want to look at it - in any case its been made 'safe').

Often electric motors have a choke near the terminals, in addition to the cap. But not always.

Chokes typically have a ferrite or other solid core material, which can store a magnetic field better than air. This just helps them absorb more energy (incurrent->magneticfield->timedelay->outcurrent) before they 'clip' and stop absorbing properly.

AtariOwl wrote:The diodes already substantially increase the resistance on the gates which is pleasing. Should i increase further?


I would remove the rectifier diodes and use 5v zeners between ground->signal as suggested above. If the currents are known to be small then you can use even lower voltage zeners providing they are somewhat safely above the TTL threshold voltage. 5v should be fine though.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Tue Aug 29, 2017 9:43 am

Hi DOug

Soooooo

While that does seem to make sense - it is unfortunately not the case. The whole thing is one big resistor/capacitor network. There are no perfect wires or connections. This becomes increasingly true as frequency and voltage are increased (both present in back-EMF!).

I'm not saying this is what is killing your joystick port - there is no way of being sure without measuring and/or guarding against it properly. However noise from the motor is certainly able to do that - even if you don't span the motor terminals.

Even if its just the same braid... within mm of each contact the motor can still feed back EMF.

OK this should plainly be addressed.


The capacitor is there to dampen the HF noise. It won't prevent reverse polarity but does help with the spikes. You'll get different kinds of spikes when the motor is running vs starting/stopping. I'd add a fast protection diode across the motor+cap which catches any voltage reversal.


I am unfortunately ignorant about diodes to a large extent. Can you point me n teh right kind of direction as to what this might be?

TBH I would instead use a zener between the signal pin and signal ground, and add a choke to each signal wire. If the signal reverses, the zener will conduct. If the signal passes zener voltage, it will again conduct. The signal is then clamped.


OK here is where i start to get confused.
If i use a zener there is a danger of reverse polarity if something freaky happens right?
I can see how that works to deflect voltage away in parallel but not for the gates.
I'm struggling over this.


However I'd also isolate if at all possible. Sudden ground potential changes are just as bad if not worse. Also the zeners can handle only a limited current before they fail. EMF shouldn't generate much current but ground potential differences certainly can.

No - either isolate fully, or ensure GND is common with minimum resistance between them. I'd prefer isolation though.


How do i isolate?


Regarding the chokes.
The motors have some small coils on the ends i dont know if this is what you mean.

Are you suggesting i should put something similar in my circuit?

I have some more 5v zeners arriving.


Sooo in the ciruit is my positioning of the diodes sensible?

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby dml » Tue Aug 29, 2017 10:05 am

Here's an example of isolation via small signal transformers. Note this isn't a complete circuit - just an explanation!

prot.png


Smaller transformers will be more responsive to faster signals. Need to be big enough to couple enough energy though for the receiving circuit.

This will ensure no DC current can get to the joystick port. It also cleans up EMF, rectifies and clamps the signal. The UF diodes soak the reverse current which will be present in any pulse. The Zener diodes clip the remaining pulse to some known range. The Zeners might be enough but more current will pass in the reverse part of the pulse so the extra diodes are there for that purpose.

The signal will be small pulses only (no DC can flow).

The two grounds are isolated - should not be joined.

(I may have got the transformer polarity round the wrong way on the output side but its easily reversed if so - won't damage anything)

The main issue here - I don't know what your sensors are, what kind of signal they produce (I assume its some kind of pulse) and how much energy in that pulse. So it is very likely that the OUT signals would need amplified with a transistor (and/or put through a schmitt trigger to make a clean digital pulse) before the joystick port. But at least its going to be safe from the electrical uncertainty at the track side.

Optoisolator can work too but you need enough current to light the leds inside those, and the leds can also be damaged. Transformers are more resilient and the most of the bad stuff is kept on one side. Main difference is optoisolators can operate DC, where transformers will only pass pulses, so the circuit design would be a bit different for each.
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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby dml » Tue Aug 29, 2017 10:31 am

AtariOwl wrote:Soooooo
Even if its just the same braid... within mm of each contact the motor can still feed back EMF.
OK this should plainly be addressed.


Taking everything into account, the common ground is more likely to be the cause. However anytime you're dealing with EMF spikes, imperfect connections, long wires, unknown and fluctuating resistances - you can't rule out spikes destroying silicon. It's better to assume its a problem and have some protection there.

Given the layout however, and the fact your motors have caps and chokes installed, the common ground is probably the main cause (as others have pointed out earlier).

I am unfortunately ignorant about diodes to a large extent. Can you point me n teh right kind of direction as to what this might be?


There are different kinds of diode for different jobs. A general purpose diode is ok, but there are very fast types (rated in nanoseconds) which are designed to catch sudden reversals or spikes - compared with, say, rectifying 50hz AC mains which is low frequency high current stuff. Different jobs.

UF4??? diodes are ultrafast and can be useful for protection. They can also carry a bit of current. There are other more modern equivalents or even dedicated protection diodes for this - I'm out of touch with the datasheets these days but UF4??? will do here IMO.

Zener diodes are just normal diodes with a low breakdown voltage. i.e. they conduct in the reverse direction beyond some threshold. For 'normal' diodes that's usually 200-1000v or so. i.e. 'infinite' for rectifying purposes. For a zener its more like 5v, to act as a clamp.

A single zener can be enough to protect against reversal and spikes at the same time, but only of the current is low in both directions and frequency isn't too high. Better not rely on that alone when motors and multiple power supplies are involved, or until you have good measurements at least.

If i use a zener there is a danger of reverse polarity if something freaky happens right?
I can see how that works to deflect voltage away in parallel but not for the gates.


Zener will conduct current safely to signal-ground when voltage goes over 5v, so the gate voltage is safely clamped at 5v.

How do i isolate?


Either optoisolators or transformers (you can wind yourself - don't need to be big, if the final output is amplified with a transistor). Either way, the grounds are not joined and no DC can flow from the track circuit to the STE.

Regarding the chokes.
The motors have some small coils on the ends i dont know if this is what you mean.


Yes that will be part of the EMF protection on the motor. That sounds ok.

Are you suggesting i should put something similar in my circuit?


Providing the motors are protected, you need to do less in your circuit (for EMF anyway). Given that you probably need to isolate the grounds the need for chokes is also reduced by isolation, especially with transformer isolation.

What you do still need to worry about is reversals and clamping, and isolating the track circuit from the STE.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Tue Aug 29, 2017 10:35 am

Hi Doug

I dont understand i will have a good look and try to understand it better... but ight now i dont get it. I dont see how the transformers will see a voltage, i dont see how it will pull the pin down.

All the sensors are is two wires one was the GND rail of the track the other a wire laying next to it but isolated from it and connected to the data pin which reads +5v until its plled down

when the car ran over the two wires it made a connection between GND and data pin pulling the pin down and regsitering a lap.


I dont understand how that part of the circuit would work.
Image

I think i can kind of see how i would separate the ADC section from the GND and live rails with the choke... but i dont understand the sensors part at all


I am so sorry i feel immensely stupid about this. It's something i never really learned about and i obviously my reading has been inadequate
Last edited by AtariOwl on Tue Aug 29, 2017 10:46 am, edited 1 time in total.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby dml » Tue Aug 29, 2017 10:43 am

I think the key part of my last answer is this:

The main issue here - I don't know what your sensors are, what kind of signal they produce (I assume its some kind of pulse) and how much energy in that pulse....


So from your last reply I understand a bit better now how your sensor works - and yes, the circuit at the sensor side would need changed to suit that. But the rest of the circuit can remain as-is.

To get a pulse into the transformer when the car passes, you could rig it to discharge a small (e.g. 0.1uF) capacitor through the transformer when the circuit is closed. The cap charges through e.g. a 100k resistor (from 22v), and discharges through the transformer. This will energize the transformer and activate the rest of the circuit.

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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Tue Aug 29, 2017 11:00 am

OK sooo

Image

This much i THINK i get.

Now the remaining issue i am not understanding is the sensors and getting teh green wire out of the circuit.
i would charge a cap across the + and GND rails. Presumably this would charge when the car is running and the V drops to 0-14v instead of 22v? It is only 22v when the throttle is wide open and the car is off teh track otherwise its about half.

Then it would trigger to discharge when the braid connectsit to GND?

I dont get it.
I still dont get how it triggers the Joystick port. Will it trigger enough? Is it going to be usually low and then go high when it triggers?

I know its my own stupidity.
I'm frustrated i thought it would be much simpler and i'm messing it up.

I feel like i'm getting more confused.


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