MC2100 input from other source instead of potentiometer to control speed.

Thread Starter

ScroungerLee

Joined Jun 13, 2020
5
I have benefited greatly from the various MC2100 discussions here. Thank you all.

I have built the circuit that uses two 555 timers, and can control the MC2100 with a potentiometer without trouble.

My end goal is to use this on my CNC mill to control the spindle motor. I use a Gecko G540 as the driver for the mill. The only spindle speed signal I can use from that is a voltage range, you give it V+, ground, and get back a voltage in the middle corresponding to the speed for the spindle. the same as using a pot as a voltage divider.

The problem is that the voltage to control that 555 circuit is reversed, in other words a higher voltage makes the motor slower. Also it seems the max voltage is right around 5 volts instead of the 12 that I get from the mc2100.

Since I am an electronics noob I am wondering how to invert the direction of that voltage range? I don’t know how to reverse it such that rising voltage from the mill driver is turned into falling voltage. Spent quite some time on google for this, but didn’t find a clear answer

Anyone?
 

Thread Starter

ScroungerLee

Joined Jun 13, 2020
5
The red wire out of the main plug on the MC2100, which iirc is supposed to be around 9v, happens to be 12v from this MC 2100. I believe others have found something similar . I will have to learn more about inverters

I can check the card to get the revision number if anyone wants


Edit: I see 12v on hdr2 pin2 to be precise
 
Last edited:

MaxHeadRoom

Joined Jul 18, 2013
21,226
In most cases it is not regulated, just the output of a bridge and cap.
There are quite a few versions of the L.V. supply and most (or all) seem to be unregulated.
I have commonly seen 13v to 15vdc in practice.
Max.
 

Thread Starter

ScroungerLee

Joined Jun 13, 2020
5
In most cases it is not regulated, just the output of a bridge and cap.
There are quite a few versions of the L.V. supply and most (or all) seem to be unregulated.
I have commonly seen 13v to 15vdc in practice.
Max.
That’s good to know since the Gecko driver for the mill has a max input of 12V, I will have to deal with that too.

I still need to learn about inverting the voltage back from the Gecko driver card. Learning is good, keeps my brain from atrophying
 

Papabravo

Joined Feb 24, 2006
14,241
To duplicate the behavior of o pot, it sounds like you need a unipolar op-anp inverter. There will be some problems with device selection and you might find a separate power supply beneficial if you need to duplicate the range of signal extremes. the reason I mentions this is than many op-amps have trouble getting their outputs to the supply rails. They can get very close but in some cases that is a "no-cigar" situation
 

MaxHeadRoom

Joined Jul 18, 2013
21,226
For some reason I somehow overlooked you are using the G540 0,+10v analogue output.
I have built some MC2100 PWM boards using a Picmicro for the 20Hz PWM, you have given me an idea on using them with the G540, a simple voltage divider on the analogue pin of the pic should do it.
Max.
 

Thread Starter

ScroungerLee

Joined Jun 13, 2020
5
For some reason I somehow overlooked you are using the G540 0,+10v analogue output.
I have built some MC2100 PWM boards using a Picmicro for the 20Hz PWM, you have given me an idea on using them with the G540, a simple voltage divider on the analogue pin of the pic should do it.
Max.
Nice, although that doesn’t address my problem as far as I can see LOL. I still need to deal with the circuit I have (the one that uses 2 555’s) having the PWM duty cycle adjustment being +5v for slowest speed and 0v for highest speed, the opposite of what the g540 does.

Or start over with some other way to create the PWM for the MC2100


BTW The G540 isn’t necessarily a 0, +10v analog output. It is 0 to whatever v you send it. It doesn’t generate any voltage. I am sure you knew that already.
 

MaxHeadRoom

Joined Jul 18, 2013
21,226
I had a 50mm square PCB made up for the pic based ones I put together, I will have to test the divider mod. I have three versions of the MC2100 here at the moment.
Max.
 
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