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Robert Brown's "MyFocuserPro2" build


JamesF
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2 minutes ago, JamesF said:

I would have liked to do that, but I get a bit antsy about it once there are polarised components in place just in case reverse voltages turn up in places they shouldn't be.

James

Hopefully this wouldn't be an issue if nothing is powered? (genuine question, I'm a beginner when it comes to electronics and the theory behind it...)

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1 minute ago, adyj1 said:

Hopefully this wouldn't be an issue if nothing is powered? (genuine question, I'm a beginner when it comes to electronics and the theory behind it...)

I have to admit that I don't know how the continuity test mode works in my multimeter, but I assume it must have to put its own voltage across the probes to see if any current flows.  Unless there's something far more clever going on that I am completely ignorant of.

James

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On most 'quality' multimeters, the continuity mode is usually also the diode check mode, which usually mean a potential difference of approx. 0.7volt for the forward current, so they tend not to be over 1-1.5 volts max, so very unlikely to do any damage to the circuit.....

Now, my dedicated continuity tester on the other hand, is a lot more robust & uses 9 volts, but then it is designed for testing long distance circuits.....

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I've just realised that I forgot to put in the current-limiting resistor for the buzzer (that's what I assume it's there for, anyhow).  Probably because it doesn't appear on the stripboard layouts which aren't always kept up to date with the most recent changes to the design.  I assume it was added later.  Fortunately there's room to move the pin header for connecting the buzzer further away from the Nano and I can just drop a resistor in across a break in the track.

James

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Finished the lid.  No photos yet, but I've run some of the tests.  The LEDs and pushbuttons appear to work fine, though the buzzer doesn't.  I wasn't entirely happy about my connector for the buzzer though, so I may need to remake that.

Next I need to connect 12V power and rig up the motors to test them.  There's a bit more work involved there though as I've decided to move away from using 5.5/2.1mm power connector plugs and switch to two pin GX12 connectors.  I don't have anything with a GX12 plug on at my desk though, so I shall see if I have enough bits to make an inline 5.5/2.1mm socket to GX12 converter in which case I can just power it from a standard 12V wall-wart.

Then I need to find some suitable four-way cable to connect up the motors.  I'd forgotten about this, I have to admit.  I suspect cat5e might actually be sufficient.  I think it should be good for an amp per conductor and the motors aren't rated that high if I recall correctly.  The only problem is that it's so awkward to work with for soldering.

James

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The buzzer probably works better with 47 or 33 ohm resistor. the resistor is to try and limit the current draw to 20mA or less. I think from memory the buzzer draws about 30mA which is a little too big for the Arduino output pin to supply. Without the resistor, the Arduino output pin driving the resistor might be damaged over time.

It also has to be a continuous tone buzzer - easy to test - if it sounds when you connect it to 5V then it is the right type - the longer lead is +ve. If it "pops" when 5v applied it is the wrong type.

The buzzer I use for a POST indication. [Power On Systems Test]

The buzzer sounds indicating that the arduino has been reset/started up. It turns off when the setup() is finished, the eeprom has been read and everything is initialized. So it tells me everything is working as it should be. If it stayed on then it indicated an issue in the setup. if it does not come on at all it indicates something is wrong - preventing the arduino from restarting. It has been very useful to me at times when making changes to the firmware.

This is basically of copy of the old PC 386 POST routines I used when making embedded PC's.

It is also used as a beep indicator for the Rotary Encoder option and to indicate when the position is set to 0 when both push buttons are pressed at the same time.

Regards

Robert

 

Concerning cat5e not really suitable. We are talking 330mA *2 (2 coils on) or there abouts. Cat5e is not rated like this and the long cables will have too much voltage drop because the wire area is too low [voltage drop is relative to wire area - thicker wire = less voltage drop]. You are better going to thicker gauge wire. You want to keep the voltage drop low. Also cat5e connectors are no good, the contact surface area is low meaning the current flows through a small surface area - causing contact erosion. You need a good amount of surface area like a db9 connector or gx12 4p connector - it will not suffer from the contact erosion that a cat5e or rj45 connector will, hence last longer and perform better. hence a rs232 extension cable is a better bet.

 

Edited by brown_rb
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I have some 24AWG cat5 patch cables that are no use to me any more, partly because they're not good enough for gigabit ethernet and partly because they're not assembled very well (they were supplied with Sun Microsystems kit, too; you'd think at the prices they used to charge they could afford to supply decent patch cables).  I've chopped a length of about a metre out of one and soldered that into a DB9 plug.  Looking at the tables for stranded 24AWG a single conductor should be good for 1.4A, but obviously the other wires and insulation in the sheath will lower that.  I think it should at least be ok for testing whilst I find something else with larger conductors.  I can't tell what size the wires are on the motor body.  No larger than 22AWG I'd say.  Certainly not as big as 20AWG.  Obviously they're in free air though.

James

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Woohoo!  It lives, Igor!

I did wonder why the tests to turn the motor an entire revolution weren't actually turning the spindle very far until I remembered that it has a 27:1 gearbox on.  Easily missed, that one :)  And I have the buttons cross-wired as compared with the LEDs, but that's just a question of switching a connector around the other way on the pin header I think.  And the buzzer now works, though I don't recall actually doing anything to fix that.

So now I need to decide which telescope I'm going to put it on and make up a suitable bracket.  Then probably re-balance everything thanks to hanging another half kilo of motor on the end of the OTA.

James

 

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Here's my "solderless" version; just now got this one assembled this morning for a 135mm lens setup

Did a couple of iterations of the enclosure "faceplate"

Also running another one I made earlier on a refractor 

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Edited by AcapulcoRolf
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  • 8 months later...

Following my adventures with PCB manufacturers I have been doing some reading - just for starters, what is the benefit of the OLED / LCD screen?

I’m presuming that’s if you’re running  “headless”.  My use would be with my 72mm frac and apt, so presumably there is no benefit having a screen? 
 

Ta

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I've not bothered with a display on the one I've built so far.  If you're at the telescope it may be helpful, but I'll be in the warm room or perhaps even in the house if I get the observatory roof automated, so for me I don't think there's a need for it.

James

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On 11/02/2020 at 11:28, JamesF said:

I did see that someone has posted somewhere about finding a match for the Baader gear, but perhaps that was actually Adrian.

James

I use the steel track on my 200PDS with a teckydave focuser. As you may be able to see from the photo it has a very useful dovetail on the body of the steeltrack to help attachment. I cut a clamp in half and drilled/taped so it could clamp into the dovetail. The belt needed is a HTD 3mm pitch all available on ebay.

20201115_193912.jpg

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