[B0SC0]

In reference to this driver board:
http://cgi.ebay.com/3-AXIS-CNC-DRIVE...item439ba474ce

Has anyone purchased the three optional pcb's for their Step Control (reduced motor current during idle) for the X,Y,Z axis motors?

How well does it work? Does it keep the motors cooler?

Thanks

[dilbert0815]

I can't talk about this specific board but I have a similar make 5-axis bord that comes with the current reduction on board.
It's working and highly recommended to have the current reduction.
If you don't do 3d milling all the time your axes schould have some idle time even during a typical routing job. This were the auto-current setting comes handy.

If you don't have the board I would suggest to do some more comparisation with other vendors for those chinese boards first. Your vendor seems notable for a very good price. However offering no optocouplers and the current control as extra seems to make the board not to appeare as real bargain..
Just from my picklist I have some other in mind you might want to compare: http://cgi.ebay.com/ws/eBayISAPI.dll...=STRK:MEWAX:IT
or the 6560 or 3977 boards from http://stores.ebay.com/verycnc

P.S. Are this hand modified wires on those boards ?
The connectors of those current extention boards also looks like hand made.
In this case I would rather buy the parts and a prefab bord and solder it myself.

[B0SC0]

dilbert0815, I would build my own if I knew what chip was used.
Looking at the pcb, it is probably just a TTL logic chip with a 14 pin package. 4 resistors, 2 capacitors, 1 transistor, 1 led, and 1- 4pin connector.
I believe it compares the ref in voltage and whether it is .8v(full current) or .5v (idle current).
If it doesn't see data from the PC, the signal goes low(.5v) after
a second or two.
I may be wrong, so if anybody can chime in,please do so.

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[dilbert0815]

Looking at the pcb, it is probably just a TTL logic chip with a 14 pin package. 4 resistors, 2 capacitors, 1 transistor, 1 led, and 1- 4pin connector.
I believe it compares the ref in voltage and whether it is .8v(full current) or .5v (idle current).
If it doesn't see data from the PC, the signal goes low(.5v) after
a second or two.
I may be wrong, so if anybody can chime in,please do so.

Almost right.
But it will not compare the ref voltage. Ref voltage is just an internal signal of the TA8435.

It's very likely a simple monostable triggered by the step clock signal.
If clock is missing for xxx milliseconds it pulls the REF pin to ground, hence changing the reference of the TA8435 from 0,8V to 0,5V. The current will change accordingly.
On my board they seems to have added a very simple RC + transistor circuit.
I guess they charge a RC circuit by the clock pulses and the transistor simply reacts once the RC circuit is discharged after the pulses go missing.
Sounds rather crude design but it seems to do it's job.

If you look for designs you may just take a look at monostable circuits with 555 chips. You get them with dozzens of different prefixes from tons of vendors, e.g. LM555, NE555,

This is another one with 4098: http://www.electronicsinschools.org/page.php?ps=2&p=932

Just watch that what you need is a retriggerable monostable.
A normal monostable would produce a pulse chain on the output with the clock present. A retriggerable monostable would have a stable output as long as the clock pulse train is faster than it's monostable time constant.

Peter

[B0SC0]

Neither the 555(8pin) nor the 4098(16pin) are 14 pin devices.
And I would think it would be a TTL chip.
Any ideas?

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[B0SC0]

Perhaps, a CD4047B would fit the bill.

14 pin soic, retriggerable monstable.

B0SC0

[B0SC0]

How about a missing pulse detector using the CD4047B?

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[dilbert0815]

I guess any of those will do.
I thought you ask for alternative instead of reverse engineer their exact circuit ?

This isn't exactly rocket science and as long as the circut detects the stopped clock pulses any circuit will do, provided that it works with the supply voltage on the connector and provides the correct polarity signal for the REF pin.

Peter

[B0SC0]

I never asked for an alternative, just if it the original worked good.
You sparked my interest in building my own idle current board.
I figured that using what he used would make it compatible.
I have these parts on hand and thought I would give it a shot.
I am just concerned with the timing and voltage levels to make it work with what he may have used.

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