5v supplies for breakout board

**cropwell** · 11-11-2014

A couple of months ago I bought a new BoB to replace the fried one originally from MD. The original has been discontinued, so I can't get a plug-in replacement. This is the one I bought http://www.ebay.co.uk/itm/Cnc-Router.../261633467531?
The doubt that I have is that I intend to connect it to the drivers in common anode mode, but the 5v for this is derived directly from the USB connection (from my computer). I would have expected this 5v to be solely to drive the opto isolators on the PC side. The stepper drivers being given 5v derived from the 12-24v input to the board.

I am a bit wary of putting 5v directly from the computer to the drivers (Tonman PD2064M).

I would welcome advice on this as my confidence has been lowered when I found the direct connection.

My machine has been out of action now for months and, due to illness, I haven't had the mental energy to put it back together.

Cheers Mates,

Rob

**graffian** · 17-12-2014

Originally Posted by cropwell

I am a bit wary of putting 5v directly from the computer to the drivers (Tonman PD2064M).

I would welcome advice on this as my confidence has been lowered when I found the direct connection.

Rob

I have a 24V power supply and rather than regulate down for some pcb's I am considering running a 5v from my PC power supply. Not being to electrical I can't see any reason not to.

**cropwell** · 17-12-2014

The purpose of the opto isolator is to prevent any damaging voltage getting to the I/O pins of the LPT port. You could connect directly from the port to the driver, but it is risky. If you get computers cheaper than decent BoBs then it might make sense to wire directly to the driver. 5v from the computer usb port should only provide power to operate the output pins from the computer. Take no notice of the Line designations, that is only relevant for printers, but the output pins(->) should be isolated with 5v power taken from the computer. The input pins (<-) should be isolated with their 5v supply taken from an external supply.

In the end most things will work, but the risk factors are different.

Cheers,

Rob

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