converting analog slotcar handcontroller to PWM

[slotcar330p4]

Hi,

I have an analog slotcar handcontroller ( brand fleischmann ) which is working like a 30 Ohm potentiometer. For my PWM circuit I need a 150 KOhm potentiometer ( in fact below 75 KOmh driving in one direction and above 75KOhm to drive in the other , it's designed for a train track).

How can I convert my handcontroller ( by adding a circuit only to the end of it's wires)?

here are pictures of my handcontroller. just to show you, not to modify it.

**broken link removed**
**broken link removed**

I'm driving on 12 to 18 volts ( depending on scale and cars ).

greetings,

slotcar330p4

 

[Sceadwian]

Replace the parts? Without the exact circuit diagram for your controller it's hard to say where to start from unless other users here know the circuits involved in a slotcar and RR car setup.

 

[RadioRon]

Replace the parts? Without the exact circuit diagram for your controller it's hard to say where to start from unless other users here know the circuits involved in a slotcar and RR car setup.

So, if I understand correctly, you want to make your slotcar controller look like a +/- 75K ohm potentiometer to whatever this is plugged into? Is that right?

 

[slotcar330p4]

Hi,

this is the original circuit:

**broken link removed**

and this is the PWM circuit diagram:

**broken link removed**

and I want to use the handcontroller in the PWM circuit between point A and d.

the PWM circuit is a very simple one but works almost the same as the more complicated ones.

greetings,

slotcar330p4

 

[rjvh]

I don't see the problem.
if you just make that circuit than it works like you want it or not??

What is your experiance level with electronics ????

Robert-Jan

 

[slotcar330p4]

Hi,

no, because I want to use my handcontroller to control the speed of the car, and my handcontroller is just 30 Ohm , the potentiometer in the PWM circuit is 100 KOhm, so I can't just switch them. I need some circuit between them.


my level of experience is about 27 years, mostly digital circuits. building circuits is no problem, designing is.

greetings,

slotcar330p4

 

[Boncuk]

Hi slotcar330p4,

as far as I know those speed controllers have straight sliding pots (no rotary type pot). Try to find one with about the same mechanical dimensions and use the 100KΩ pot. The drive current won't pass via the pot but via the thyristor.

Boncuk

 

[slotcar330p4]

Hi Boncuk,

the handcontroller has indeed a straight potmeter, it is a wired one , not standard and I don't want mess with the handcontroller except connecting it to a circuit which will be connected to points a and d.

greetings,

slotcar330p4

 

[slotcar330p4]

So, if I understand correctly, you want to make your slotcar controller look like a +/- 75K ohm potentiometer to whatever this is plugged into? Is that right?

yes, in some PWM circuit it is 150 KOhm, some other 100 KOhm, some for driving in one direction only, some other to drive in both ways.

greetings,

slotcar330p4

 

[philba]

The easiest solution is to find a replacement pot that will fit your hand controller. Probably impossible.

I'm sure this will be more than you want to bite off but I would use a microcontroller to measure the hand controller voltage (use the pot as part of a voltage divider) and the micro would generate the appropriate PWM duty cycle which then drive a mosfet.

You might be able to make something like what you want to happen with a small mosfet operating in the linear region to replace your 100K pot. The hand controller divider would drive the fet.

By the way, I wonder if the triac in your "PWM" circuit will work correctly with a full bridge rectifier.

 

[slotcar330p4]

Hi philba,

your idea is correct, but my first intension was to make it with just standard parts, not programmable ones. but if you don't succeed with plan A, skip to plan B. but I want to try plan A for now.


greetings,

slotcar330p4

 

[Boncuk]

Hi slotcar330p4,

if you measure the overall lenght of the pot to be replaced I'm probably able to help you out and send you some pots.

My local electronics shop has several hundreds of short type sliding pots (industrial overproduction, estimated 1 - 1 1/2"), and may be that kind would fit into the grip.

Of course the original pot must be wired since the entire motor current flows across the pot, hence power.

With the PWM circuit a standard value of 250 to 500mW pot is sufficient.

Boncuk

 

[Boncuk]

By the way, I wonder if the triac in your "PWM" circuit will work correctly with a full bridge rectifier.

Hi philba,

the triac is a thyristor. There should be good chances for it to turn off since the rectified and unsmoothed DC also "oscillates" between max positive and zero.

However I admit, that the circuit is no elegant way.

Boncuk

 

[slotcar330p4]

hi boncuk,

I appreciate your help, but I don't want to change anything to the handcontroller,

just put a circuit to it's wires and the circuit to PWM-controller.

greetings,

slotcar330p4

 

[Boncuk]

Hi slotcar330p4,

in that particular case don't change anything. The PWM circuit won't work with a 30Ω variable resistor.

Boncuk

 

[slotcar330p4]

Hi Boncuk,

I know, that's why I need a converter.

greetings,

slotcar330p4

 

[OutToLunch]

instead of the 1uF capacitor, you could try a 3300uF cap. It would give about the same time constant...

 

[slotcar330p4]

hi OutToLunch,

it might give the same time constant, but with only 30 Ohm there is not much variance in speed.
( I even think not at all . . .).

greetings,

slotcar330p4

 

[xilix3]

From my (very rusty) understanding, in your PWM circuit, the value of R1 determines how quickly the voltage at point d rises to the level required to turn the transistor on.

Perhaps you could use the 30 ohm pot to control a current source connected to point d.

Cheers,