Replace old DC motor hand-controller with PC control

Hi All,
I have an old telescope with an in-built focusing motor. The motor is operated by a wired hand-controller powered by 4 x 1.5V AA batteries. I would like to have PC software control of the motor, but I don’t want to rip out the existing in-built wiring to do so. Ideally I would like to be able to simply unplug the mini 4-pin DIN connector of the hand-controller and plug in a controller with a USB interface.
My issue is the hand-controller uses four wires - two for each motor direction ie focusing in and out. I’m not sure how to go about using the existing four wires that lead to the in-built PCB (a 5V 2606AD JRC 5004B) and then to the two wires that run the motor.
The motor is an old Faulhaber 1624E003S, which I believe has an operating voltage of 0.2-4.8 V.
Any suggestions would be greatly appreciated.

Hi Jason,

Welcome to the forum!

I’ve got a rough idea of how your device works, and I’ve found a datasheet for that motor controller (attached below), but I’m not sure how everything is connected. Could you post a photo of the internals so we can take a look at the wiring and PCB?
njm2606-datasheet.pdf (187.0 KB)

In the meantime, depending on how it is wired, Liam’s guide on using an analog switch IC to emulate button presses may be helpful:

Keen to get this project on track with you!

Hi James,
Thanks for the info. I’ve attached some pics.
Hand control internal
Motor PCB

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Hi Jason,

Thanks for sending those photos through. It looks like the PCB is responsible for stopping at the limits of travel, and speed control of the motor, and the switch box is responsible for sending forward or reverse voltage to the rest of the circuit (I think).

There are a few methods you could go down here, in ascending difficulty:

  1. Replace the PCB and switches with a USB motor controller, such as the Pololu Jrk:
    Jrk G2 21v3 USB Motor Controller with Feedback | POLOLU-3142 | Core Electronics Australia
    These are quite pricey, but would avoid working with the existing system, and I don’t think it supports end stops, so you might need to set a current limit or something like that, I haven’t used this bit of kit myself

  2. Use a microcontroller like a Raspberry Pi Pico and a couple of relays to complete the connections usually made by the switch: 5V Single Channel Relay Module 10A | Core Electronics Australia. From there, you could write a GUI in PyGame that runs on your PC and sends commands over serial to the Pico to actuate the motor.

  3. Same as above but using a motor driver to replace the PCB and switches entirely. This would allow speed control from the software if you wanted it, but you’d still need to implement your own endstops.

Keen to hear your thoughts on the above!

Thanks James,
At this stage, I don’t want to replace the in-built PCB as I would like to keep the option of using the battery hand controller on occasion. So, it looks like option 2 best suits me. I’ll search up some info on Pi Pico and work out what I need to buy from you.

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Hi Jason
I think James is correct in saying that board provides limit or end of travel switching as there is a micro switch at the board ends. This makes me think the whole board moves with respect to something else. From the pics it is a bit hard to figure out what that something else is. It would appear the outside cover would have to be on to allow the outer switch to operate.

That beige coloured device on the board I think is a relay. Can’t read anything much of the numbers except for “5V”.

What do the switches on the controller do.?? I think probably just direction and start/stop with no speed control. Push button or toggle??

I don’t quite see what you are trying to do here. If you are trying to introduce a PC for focus drive what is going to tell the PC what is needed. You will still need something to tell the PC to go forward and reverse and to activate the motor. The only advantage here is you may get some speed control but if the existing system works in a satisfactory manner you are only going to add complexity.

This could actually be done with an Arduino. Single potentiometer for speed and direction control. Centre being off, clockwise rotation one direction and anticlockwise rotation the reverse. I have found that a relay for voltage and thus motor reversal to be best as unless the later ones have changed the solid state “H” bridge drivers don’t allow motor “creep” at a very low speed from standstill. They tend to start with a bit of a rush (about 20% of full speed) and then can be backed off but for focus control or similar this would not be ideal. There is a reason for this which is a bit long winded to go into here. I have brought this subject up before with an offer to elaborate if anyone was interested but generated no queries so did not bother.
Cheers Bob

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Thanks Bob,
The beige device is a signal relay (G6J-2P-Y) and yes, the limit switches (D2F-01L-A) require the cap to be on and stop the motor moving too far out or in when focusing - the motor moves the secondary mirror on a Dall-Kirkham reflecting telescope facilitating fine focus after the primary mirror has been focused coarsely, if you’re curious. The reason for PC control is to enable fine focusing remotely when imaging planets or the moon. Currently this can only be done by using the hand-controller whilst standing next to the telescope - a cold job at this time of year!

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I’ve attached a pic of the hand-controller showing the push buttons - the motor starts up slowly and then reaches top speed if a button is held down.
Controller buttons

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Hi Jason
That makes a bit more sense. Just googled “Takahashi” which was pretty enlightening. Seems they make some very high end telescopes. Personally I have not heard of them which is not surprising as I am not really up on that sort of thing.

If you envisage operating this focus by existing means or PC my suggestion would be to use a couple of small relays. Connect the N/O (normally open) contacts directly across the switch contacts in parallel with the existing wiring (leave that in place) and operate the required relay with some electronics like Arduino, RPi etc. Possibly via WiFi or bluetooth remotely if you wish. I will leave that to the Gurus.

If you do this you will be able to leave the existing electronics in place with limit switches etc.
Additional relays and electronics might be a bit much for AA batteries so you might have to revise your power arrangements.

You might want to think about some sort of “Local/Remote” switching so if a button is accidentally pushed while in the “Remote” mode nothing will happen or vice versa. Just to prevent any possible damage to what is probably a pretty expensive bit of kit. This would be only a bit of a wiring modification so would not interfere with system development and involve the addition of probably a DPDT switch.
Cheers Bob

Add on: I note the wires leaving the board are Brown, Red, Orange and Yellow. When the cable arrives at the other end (where the buttons and battery are) they seem to have changed colours and it is difficult to see exactly what goes to where. I realise this is probably due to the difference between natural light and flash but if you could separate the wires at the button end and take a pic with natural light it would make it a bit easier to see exactly how this is wired.

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Hi Bob,
That’s a great idea to wire the relays via the hand-controller contacts. The wire colours are different between the hand-controller cable and the wires that are built into the telescope tube. The HC cable connects to the tube via a mini 4-pin DIN connector - see pic.

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Hi Jarrod
That would explain that. BUT without knowing this just how was anyone going to be able to establish what each connection does. I have said it all before that getting enough information to provide any help is like pulling teeth. Probably why you are not getting many replies.

NOW what does each wire look like at the other end.
Cheers Bob

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Hi Rob,
The other end of the wires are shown in the first two pics above. After tracing them, I’m relatively sure the Red and White wires of the HC are both connected to battery positive, depending on which button is pressed and Black and Green return from motor to battery negative. Red and White wires become Red and Brown after mini 4-pin DIN on telescope and connect to motor PCB. Green and Black become Orange and Yellow and connect to ground of PCB.
Given that circuit, what’s to stop the motor shorting if both buttons are depressed at the same time? Does it look like there’s something on the PCB to stop this? Just wondering if I use two relay channels and there’s a delay in opening/closing one, could I short the motor?

Hi Jason

Being RELATIVELY sure instead of POSITIVELY sure can result in that expensive green and yellow smoke commonly associated with mistakes. Let us be a bit positive shall we.

An accurate sketch would work wonders. Forget about what happens when the switches close, just sketch a circuit with both switches open. At the end of the day the voltage on the motor has to be reversed to get the motor to turn the other way. The switches obviously have something to do with this.

What circuit, haven’t seen one yet.

Don’t know, will comment when I seee a sketch of the wiring.

I would be surprised if that could happen, but don’t know.

There will be a delay in both releasing and operating a relay. Depending on size and type (this varies) typically this delay is in the order of 10mSec. If you have any concerns use DPDT relays and they can be wired so to be impossible for both to operate at the same time. As far as shorting the motor goes if operating both switches does no harm then operating both relays will be the same.
Let’s see that ACCURATE (no relative sure business) s circuit sketch.
Cheers Bob