Motor control

[Andrew Davie]

This area of the televisor has been my absolute nemesis...
Now, however, I'm going to be supplying the motor with 12V (give or take) instead of the 22V it was getting before.
Hopefully my disc will spin at something less than 10000rpm this time.

[Harry Dalek]

This area of the televisor has been my absolute nemesis...
Now, however, I'm going to be supplying the motor with 12V (give or take) instead of the 22V it was getting before.
Hopefully my disc will spin at something less than 10000rpm this time.

Its funny as every motor is a touch different what will work on one will not work on the other ...with the PMT camera i had nothing but trouble .i am still trying to work out why the 4046 just refused to cooperate .
I just went back to using the 555 bistable which is a touch more simple ..hard to say what will work every time i try its always trial and error but for me i have had more luck with the bistable over 4046.

[Andrew Davie]

speedctrlCKT2.gif (6.12 KiB) Viewed 14399 times

I believe the above circuit is from Klaas. I am not exaclty sure I understand the 4011 section.
Other IC stuff I have seen has always had a "black box" approach with the IC number in the box. This is a little different.

I want to make sure I understand. In the 4011 area in this diagram, do I connect pins 5 to 6, connect a 1M resistor from those to pin 3. And I connect pins 1 to 2, and then to 4?
Is this just trying to show me I could use alternate parts (two NAND gates) instead of the 4011?

[Klaas Robers]

Correct Andrew. In fact two gates of the 4011 are used as an inverter. That is done by connecting both inputs together. You might also use a NOR circuit, or just CMOS inverters. Be aware that this is a CMOS circuit, it runs on 12 volt. TTL-IC's dont, neither do 74C..... circuits.

This circuit is a so called Schmidt trigger. The output is always "zero" or "one". When the input signal rises slowly, which is always the case when it is coming from a mechanical movement, the output goes to "one" suddenly. So the output of this circuit gives a steep binary signal. When you simply amplify the input signal, you can get some form of oscillation at the transient position. The 4046 reacts on this oscillation as if it has seen many holes in the disc. That is the reason that the Schmidt trigger is in the chain.

[Andrew Davie]

Correct Andrew.

Thanks! I am building this circuit as a drop-in replacement for my "old" motor driver. It's on a separate board.
I am learning how to make things easier for myself - screw-in headers on boards dedicated to one task only. If something goes wrong I can easily replace.

[Andrew Davie]

I have built the circuit. I gravely misjudged the size of the board I would need, and I used a very small perfboard-type just 6.5 cm x 4.5 cm including margins. This has a few "ground" and a few "12V" lines so the holes aren't arbitrarily useable. It took me most of 2 days to figure out optimal spacing and routing for the components. I make things hard for myself. Anyway, it's a mess underneath - my 40 W iron isn't the best and I occasionally had to "undo" stuff. But anyway, complete and on to testing.

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I did not connect the sync line. I used an IRF540 instead of an IRF510.

Power applied, the LED lights. Good - at least I remembered how to wire LEDs the right way

The motor runs. I provided a power-out terminal for the motor where the GND is from the control circuit, but the 12V is the power from board input. The idea is that the 12V connection is optional to this board, or some other source (say, 20V) can be used if the motor needs more voltage. Normal usage would be to only connect the GND on this board to motor, and + to the other source.

You can also see one arm of the IR-sensor mount that I finished designing/printing today. It's OK - not pretty, but holds the TX/RX aligned with adjustable spacing. As you can see with the picture, the IR transmit is working, but it is quite dull. I'm coming to the realisation that I'm really not going to ever be able to do analogue electronics. I don't spend enough time on it, and I'm really just being a soldering monkey copying circuits that take me ages to understand. I have been thinking about the Arduino solution and I instinctively know pretty much all I need to to to get that running and it's so simple. This has taken decades of my life.

Anyway, moving on... I tried it again to test something and now the motor ISN'T running. Strange, I have clearly already blown up something

[Klaas Robers]

I think you didn't. If there are no sync pulses going to the circuit, the motor is not running. As soon as there are sync pulses, the motor will try to get pulses from the IR-fork as well. This happens too in the MUTR televisor, which uses the same circuit.

But have you already tested that you get pulses out of the IR-fork? Pulses that are high enough to trigger the 4046? Or even better: high enough to trigger the Schmidt trigger (4011)? That you should do first. Don't bother yet about a running or not running motor.

And then, when this is all Ok: remove the 4046 from its socket and see that you get the motor free running at the optimal speed. Of course it is not synchronised, but that is a next step. Proceed step by step. That is something you should have learnt from building your first monitor......

[Andrew Davie]

I'm an idiot, in that I (after a much-needed few glasses of wine) tested the circuit with rectified 12VAC. Yeah, I was feeding it 17V.
Bah. It's probably fried. Will do some diagnosis tomorrow.

[Klaas Robers]

I see that you did not use sockets for the ICs, so removing the 4046 is not an option.

Don't be desperate. Big chance that the CMOS circuits survived this. Yes, they are specified to work between 3 and 15 volts, but that does not say that they die at a lousy 17 volts. I expect that they can have as much as 25 to 30 volts. Consider them as undamaged and do your tests, one by one.

- Do not yet connect the motor. This is for the next intruction e-mail.

- Power the electronics part from the stabilized 12 volt.
- Then first scope the output pulses of the IR-detector, with the disc in between. So mount the fork, look at the voltage of the sensor while you rotate the disc by hand. Adjust that for a voltage swing of e.g. 3 to 9 volt. You should adjust the variable resistor (100k) to get this optimal.

- Then go to the output of the Schmidt trigger, the input of the 4046 (pin 3) and see the 0 volt and +12 volt while you turn the disc. If needed solder a short piece of wire, or even an eyelet, against pin 3 of the 4046 to clip your scope on. Observe that this voltage changes suddenly, never slowly (turn the disc slowly). Nice.

- Now you have done the part left of the 4046, time for the next step.

[Klaas Robers]

I refer to your circuit of this thread 28 feb (above). I see there a jumper, called "Close Loop", from pin 13 of the 4046 to the "damping" potentiometer (220k). Is this jumper the black push button? Is this a push button that is normally opened and only makes contact when push? You can find this out with your multimeter. Most of these push buttons are of that type. In this case: remove it. You should have a pushbutton that interrupts when pushed, but for the time being a jumper (two pins with a small block that connects both pins) or an on-off switch is better.

- Remove the small jumper-block, or put the switch in the "off-state".
(- If you had an interrupting push button, you have to push it continuously for the next few hours. Bad idea.)
- Set the potentiometer of 10k in the centre position
- Connect the disc motor and power up the motor.
- You can see that, when the switch is "off", the 4046 is not at all connected.
- So there is no need to power the 4046-4011 as well, but it is also not forbidden.

- The motor should start running at a certain speed.
- If you adjust the potentiometer of 10k the motor should run faster and/or slower.
- If the motor cannot be spun to 12.5 rps, the voltage on the top (+) of the motor is too low.
- It is a good idea to fix a stroboscopic disc to the Nipkow disc. Now you can see the optimal speed.
- Measure the voltage on the bottom (-) of the motor (in respect to "ground").
- This should be about 6 to 8 volts.
- By the way, do you know what voltage the motor needs for a correct speed with the disc connected? Tell me.
- Don't jump over to the end by closing the switch, hoping that it works, then you learn nothing.
- We do this step by step.

[Andrew Davie]

I refer to your circuit of this thread 28 feb (above). I see there a jumper, called "Close Loop", from pin 13 of the 4046 to the "damping" potentiometer (220k). Is this jumper the black push button? Is this a push button that is normally opened and only makes contact when push? You can find this out with your multimeter. Most of these push buttons are of that type. In this case: remove it. You should have a pushbutton that interrupts when pushed, but for the time being a jumper (two pins with a small block that connects both pins) or an on-off switch is better.

- Remove the small jumper-block, or put the switch in the "off-state".
(- If you had an interrupting push button, you have to push it continuously for the next few hours. Bad idea.)
- Set the potentiometer of 10k in the centre position
- Connect the disc motor and power up the motor.
- You can see that, when the switch is "off", the 4046 is not at all connected.
- So there is no need to power the 4046-4011 as well, but it is also not forbidden.

- The motor should start running at a certain speed.
- If you adjust the potentiometer of 10k the motor should run faster and/or slower.
- If the motor cannot be spun to 12.5 rps, the voltage on the top (+) of the motor is too low.
- It is a good idea to fix a stroboscopic disc to the Nipkow disc. Now you can see the optimal speed.
- Measure the voltage on the bottom (-) of the motor (in respect to "ground").
- This should be about 6 to 8 volts.
- By the way, do you know what voltage the motor needs for a correct speed with the disc connected? Tell me.
- Don't jump over to the end by closing the switch, hoping that it works, then you learn nothing.
- We do this step by step.

Thanks Klaas.
It is 1:41am here so I will just answer a few points, but no testing/changes until tomorrow.
The black push button IS the one you have identified. It occurs to me now that I did not test it, but I was very specific when buying that I wanted a "normally closed" button - that is, one which is ON when not pressed. But you know, I should have tested, right. Mmh.
Many thanks for your support/comments.

[Klaas Robers]

Good. I know it is too late for you. It is here in the middle of the afternoon, so time enough to give you the first instructions and feed back.

- Check the wirening of the IRF540 transistor. The pins towards you, numbered 1, 2, 3:
1 = the gate (base of a normal transistor)
2 = drain (collector of a normal transistor) goes to the motor.
3 = source (emitter of a normal transistor) connected to ground.
- If needed, search on the web "IRF540 pinout".

- Find yourself a so called jumper, two pins with a small shorting block.
- Mount that in series with the "normally closed" push button,
- such that you can do experiments with the push button continuously pushed without pushing it all the time.
- See also the second step in between brackets, in my previous post.

- Another solution is to change the pushbutton for a light brown connection block.
- The push button with short wires (clipped off resistors) screwed into this block.
- Later the push button can be positioned on the front, for obtaining manual frame sync
- and connected with longer wires to this connection block.
- Experiments with the motor control can be done by connecting nothing.

[Andrew Davie]

- Check the wirening of the IRF540 transistor. The pins towards you, numbered 1, 2, 3:
1 = the gate (base of a normal transistor)
2 = drain (collector of a normal transistor) goes to the motor.
3 = source (emitter of a normal transistor) connected to ground.


- Find yourself a so called jumper, two pins with a small shorting block.
- Mount that in series with the "normally closed" push button,
- such that you can do experiments with the push button continuously pushed without pushing it all the time.
- See also the second step in between brackets, in my previous post.

- Another solution is to change the pushbutton for a light brown connection block.
- The push button with short wires (clipped off resistors) screwed into this block.
- Later the push button can be positioned on the front, for obtaining manual frame sync
- and connected with longer wires to this connection block.
- Experiments with the motor control can be done by connecting nothing.

I was VERY careful to get the pinouts right on the IRF540. Nonetheless, tonight I will re-check.
Per the diagram above, I connected the source at bottom, the gate at the sideways middle part and the drain at the upper part.
I will reconfirm in a few hours, but pretty sure I have this correct.

As to the pushbutton, I should be able to just tape it down to keep it open-circuit, right? A bit of hot glue or tape or something. I'll also check with a meter to make sure it's doing what I think it's doing (that is, closed-circuit when not pressed).

Now I understand your last "connection block" idea, that's actually a pretty neat solution and I might do that.

[Klaas Robers]

Andrew, i am writing a short tutorial for you about motor control. I am going to place this in my own webspace, but you can get it (.pdf) from here. The advantage is that I can update it for a newer version without editing this page. At this moment I am not yet finished with it, but you might already load it down, read it and try to understand the theoreticals (not so difficult) behind it. During the coming days it might expand.
You may find it at http://www.prof.robers.nl/forumfiguren/tutorialmotorcontrol.pdf.

[Andrew Davie]

Andrew, i am writing a short tutorial for you about motor control.

Great, I will definitely benefit. Very kind, TY. I haven't done much today about your earlier tutoring/advice, as I gave blood and that didn't turn out too well (again). My BP plummeted to 91/61 and been in bed most of the afternoon/evening to avoid falling flat on my face. The Arduino stuff I can do with a laptop on my lap... in bed