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

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

Postby dml » Tue Aug 29, 2017 11:01 am

Here's a new version which triggers the transformers when the cars close the SW1 or SW2 circuit.

ver2.png


Someone better than me can optimise this/simplify it - but this method will be safe and should work ok.

You can make the transformers by hand using a few turns on small ferrite rings - they don't need to be large, especially with the capacitor arrangement here, plenty of energy available.

The capacitors charge slowly via 100k resistor. When the SW1/SW2 switch is closed with track GND, the capacitor discharges through the transformer and the charge cycle restarts. You can optimise the resistor/cap sizes for best results (recharge time vs energy to transformer).

I didn't calculate anything properly but its probably a good stab at some values.
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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby dml » Tue Aug 29, 2017 11:20 am

Unfortunately it seems CircuitLab is no longer 'free' so it threw up a membership banner, then logged me out and I just lost that circuit diagram. The joys of 'cloud'.

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

Postby dml » Tue Aug 29, 2017 11:54 am

BTW I forgot to add - there are other, implicitly isolated ways of detecting the cars.

You could use a hall-effect sensor (small magnet attached to each car, passing a coil) or a LED arrangement where the LED reflects light back to an adjacent photodiode or equivalent, when the car passes on top. Both of these don't need connected to the track circuit, and probably involve fewer parts than full isolation.

Every method has its own weird problems but all can be worked around. e.g. the hall effect (or other magnet) sensor wont detect a really slow moving car. The led method might get confused by other light sources, and needs a white or metal reflector spot under the car. etc. The method I suggested might have problems detecting cars that don't contact the sensor switch properly - the cap needs to discharge properly to trigger the transformers.

Hopefully you'll get success with one of these. At least they wont fry the STE with random voltages.

I assume you're going to get the buffer chip (or whatever it is thats driving the port) repaired in 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 12:13 pm

There are other methods
I dont want to use dead strip as it has the same problems as this method AND has a dead section of track
The LED system wont work as i run two lanes very close together in an AC2car arrangement.
I cant use optic sensors in the track for the same reason plus that its routed and already built.

I dont know if the cao will charge enough to trigger this.

I dont know about replacimng teh chip as i was thinking of using the pins that arent fried but maybe thats dangerous because its already dodgy.

Unfortunately to a large extent i'm not getting it.
I had in my mind a simple system based on split dead rails that other people seemed to be using without much difficulty and i'm clearly not getting it to work.

I am very limited on equipment, and on knowledge and i'm getting more and more confused and disheartened.

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

Postby AtariOwl » Tue Aug 29, 2017 12:16 pm

OK

So i need t make 6 transfromers

i have no idea what the cap will charge like with the much lower voltages going through the car.

Its so sad.. for 50laps the system as it was was beautiful ... then ZAP

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

Postby AtariOwl » Tue Aug 29, 2017 12:25 pm

OK i just need to calm the hell down and approach it logically

1 - need to make 6 transformers
2 - need to get the right caps to be able to cope trigger the counter. I'm really uncertain about this, the connection was so simple this is getting more and more complicated
3 - the connections to the pins still make no sense
will they be 0 normally and go high when they are triggered? How does this work with the EJP which has high omn the pins until something pulls them to ground?

If the car only goes over for a tiny fraction of a second is this going to be enough to trigger the cap enough?

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

Postby dml » Tue Aug 29, 2017 12:52 pm

I'd start with one small hand-wound transformer with e.g. 22 turns on the track side, maybe 6-7 turns on the STE side (which will step 22v down to approx 5v with some extra margin) and tweak the number of turns to get the it working - get a confirmed detection. Once that's good, make the other transformers. Otherwise you'll just waste more time.

The capacitor delivers the impulse. 0.1uF-0.5uF should be enough if contact is good. I wouldn't increase this too much unless you are certain its preventing detection. The transformer transfers the pulse safely from one circuit to the other. By tweaking either transformer or capacitor you'll get your signal. The rest is just some protection diodes.

As mentioned above I might have arranged the transformer outputs the wrong way around (note the dots on the transformer symbols) but you can swap the wires around if needed. If it is the wrong way around the pulse will just disappear through the UF diodes - no harm done. You can test the output using a LED in a darkened room. It will flicker more visibly when you close the circuit, if the transformer polarity is the correct way around. Or better use a scope if you have one.

Normally you would couple a circuit like this to digital using a transistor/buffer but providing your zeners are in place and given you've got a 22v pulse into the transformers you shouldn't need amplification - just decent protection.

You can also slow down the pulse if necessary by adding a few ohms in series with the capacitor. If you do so, you may need to increase the number of turns on the STE side of the transformers to compensate a bit.

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

Postby dml » Tue Aug 29, 2017 1:06 pm

AtariOwl wrote:1 - need to make 6 transformers


I'd start with one. Otherwise you will end up with 6x the mistakes while getting it to work.

AtariOwl wrote:2 - need to get the right caps to be able to cope trigger the counter. I'm really uncertain about this, the connection was so simple this is getting more and more complicated


Any capacitor should do but I'd stick with ceramic or polyprop types because they can discharge very quickly. You can use a small value electrolytic but only if you start needing values of 1uF or higher - and then you need to make sure the polarity is correct. I'd start with small ceramics.


AtariOwl wrote:3 - the connections to the pins still make no sense
will they be 0 normally and go high when they are triggered? How does this work with the EJP which has high omn the pins until something pulls them to ground?


I didn't really provide a circuit for coupling to the pins - haven't looked at it at all. But you can rig it to work either way.

If the pins are active-low, you should connect a NPN transistor so when the +5v pulse arrives, it will turn on the transistor and pull the pin low. This is quite a common arrangement for coupling signals to logic.

If the pins are active-high, then you can just connect a 1k pulldown resistor to the pin so its 0v until the pulse arrives.

AtariOwl wrote:If the car only goes over for a tiny fraction of a second is this going to be enough to trigger the cap enough?


It won't take much time for a ceramic cap to discharge through a small impedance. This is one of the reasons you don't want to use a large capacitor. Better keep it small, let it discharge quickly, and use the transformer turns ratio to ensure the signal is adequate at the other end.

You can also test all of this without the STE being involved. Better with a scope - but you can do it with a LED connected to the transformer outputs in a dark room. If you see the LED flicker you know there's enough voltage/current present to activate the port with protection in place.

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

Postby AtariOwl » Tue Aug 29, 2017 2:26 pm

i dont have a scope. I do have LEDs maybe thats something i can look at.

I think in essence i need to calm down, not try to get this done quickly and approach it in a methodical manner.

In order to start the transformer should i just buy an iron torus to get myself started?


I'm guessing this is the start of a fairly length road instead of teh simple connection i had envisaged

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

Postby dml » Tue Aug 29, 2017 2:45 pm

You can find small toroids in dead power supplies, CFL lamps, PCBs for display backlights and other common electronic scrap. That's where I generally get them from. However you want to make sure you can find several the same size. We're talking 1cm diameter probably. Not big things.

Still I'd start with scrap, get it tested with one sensor, then find several of roughly the same size and type and retest with one of those, then duplicate it out as many times as needed.

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

Postby AtariOwl » Tue Aug 29, 2017 3:32 pm

HI DOug

I REALLY appreciate this... this is the help i need, i just got a bit daunted, once it becameobvious there wasnt a quick and simple fix.

All teh Best
Joe

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

Postby dml » Tue Aug 29, 2017 3:40 pm

No problem - I'll have a play with CircuitMaker later if i can, and see if I can get values correct for a first try. The simulator should be good enough for a test (well nothing ever works first time but you always find something out along the way ;)

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

Postby AtariOwl » Tue Aug 29, 2017 4:05 pm

Will it be ok if we keep working through it here?

I am ignorant, i'm fully aware of just how ignorant i must be about this... but it could prove useful to somebody else so i think working through it here would .... well i need working through from basics, because i'm starting from such a low position.

Especially the timing. I fear my sensors womnt work they are short about 2cm which was fine for the direct connection but i have my doubts if its using the cap.

I downloaded circuitmaker but its daunting to begin with.

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

Postby Omikronman » Tue Aug 29, 2017 4:35 pm

I can not imagine what causes that much problems. I remember there was one cable of the joystick port that had to be connected with one of two others dependend on which joystick direction signal should be told. Impossible to wreck it that way?! I made a slot car software myself some time ago. We gave it a first try at the OFAM 2014 I think:

look at 04:26:
https://vimeo.com/107422896

The LapTimer:
https://vimeo.com/102247011

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

Postby AtariOwl » Tue Aug 29, 2017 4:55 pm

I was so hoping it would be something simple.
And that the connection would be simple enough i could cope with putting it together myself.

I should point out i'm using the EJP not the standard Joystick Port as i had intended to use the ADCs to monitor throtlle position to calculate 'fuel' usage and synchronise sound.

The coding has gone pretty well... the connection... NOT.. at least not once the cars are running. It works for a few laps.. then kills a pin.

The project is
Image

Timing software i had working just fine on teh track as long as the power was not connected.
Once it was connected i started killing pins


The software times, scales it up to the track and then displays it liek a pitboard.
No pic sorry.

Then it shows practice times, race results and a lap by lap chart
Image
Image
Last edited by AtariOwl on Tue Aug 29, 2017 5:05 pm, edited 1 time in total.

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

Postby Omikronman » Tue Aug 29, 2017 5:02 pm

Well, I only made the software while Christian Hellmuth modified the start/finish part of the track to recognize the signals. So he should know best how it is supposed to work. :)

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

Postby AtariOwl » Tue Aug 29, 2017 5:12 pm

I'm guessing you used the standard port not the EJP?

Your software looks great.

Mine is a little less pretty in some ways.. but its designed for a certain look and to essentially run grands prix 1 car at a time

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

Postby Omikronman » Tue Aug 29, 2017 5:14 pm

Ah yes, I think we used the joystick port one. :?

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

Postby AtariOwl » Tue Aug 29, 2017 5:33 pm

i'm wpndering if that is better protected than the Enhanced one

I'm just worried at how massively more complicated the situatiomn is becoming.
I would be VERY interested in the connections you used though.

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

Postby Omikronman » Tue Aug 29, 2017 5:43 pm

I sent a message to Christian for this task. Hope we'll get a response soon. :)

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

Postby mlynn1974 » Tue Aug 29, 2017 8:36 pm

What an amazing project! I read that some slot cars use 8-18V and to allow 1-1.5A per car but this circuit has a maximum of 22V.

What would happen if 2 cars passed the detector at the same time? It's a long time since I've seen a Scelextric so I don't know if that could happen on a double track.

In general would an off the shelf Buck Converter work instead of a hand made transformer?
I read that they decrease voltage and increase the ampage with high efficiency. e.g. 22V @ 1A input could be 5V @ 4.4A output
How do you then reduce the ampage to something safe?

The main thing I have learned from DMLs excellent info is separating the high voltage inputs from the digital signal side. The Atari should be reading signals and not being exposed to dangerous voltages. Excellent work!
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Re: Please Help (Fried Pins) I think i am slowly killing my STE

Postby AtariOwl » Tue Aug 29, 2017 10:03 pm

I should point out the 22V only occurs when there is no load, once a car is present it tends to stay below abuut 14V

It utilises the Pacer units to allow pace cars to run

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

Postby AtariOwl » Sun Sep 03, 2017 5:12 pm

Could i use optoisolators?
How might i do that?

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

Postby dml » Mon Sep 04, 2017 8:41 am

AtariOwl wrote:Could i use optoisolators?
How might i do that?


If you have optoisolators you could connect the input (LED) side across the 22v/sensor rails so when sensor-0v open circuit is closed by the car, it will activate the isolator LED briefly. But you'll need a resistor (at a minimum) to protect the LED from burning out at 22v.

There are neat ways to do any of these circuits properly (opto or magnetic) so you get a fixed pulse length (or just invert the signal on each crossing) - which makes for better detection. But you can start with just a resistor to protect the LED.

Lets say 22v for the supply, 5mA for the LED (but you need to check the optoisolator datasheet).

Use Ohms law:

http://www.electronics-tutorials.ws/dccircuits/dcp4.gif

R = V / I (resistance = volts / amps)

so...

R = (22V / 0.005A) = 4400 = 4.4k resistor

So a 4.4k resistor in series with 22v will operate the isolator. However you said that the voltage drops as low as 14v depending on the cars so that no good.

You'll need to find the min and max safe operating current for the isolator from the datasheet, get the middle of that range and then calculate the resistor for that. You'll then need to check that the current is still in range for 14v and 22v extremes with that chosen resistor.

Since the isolator will only be on briefly, for the simplest kind of circuit, your margin will be bigger so you can err towards a smaller resistor to improve detection.

I doubt this is the most reliable circuit to use as-is but it is at least simple. It involves fewer parts than a transformer based one. Obviously you'll need to buy suitable optoisolators first.

An alternate version of this could have the LED on most of the time, with the sensor shorting it out. This would give you more opportunity to regulate the current so the voltage fluctuations don't matter so much. It again involves more bits though (like adding a single 12v regulator, and then a fixed resistor+capacitor pair for each isolator). There are numerous other circuit variations which will also work.

You can improve reliability in similar ways to the transformer circuit - cleaning up the trigger or fixing the pulse length for detection. Just be careful not to toast the LEDs using the wrong resistor values.

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

Postby AtariOwl » Mon Sep 04, 2017 9:56 pm

How about this?

I need to try to keep things simple for my old brain to cope.

Image

Am i on the right track?


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