G203V Opto Polarity - Why?

[Clockwork]

I have both G201 and G203V drives. It's been bugging me why Gecko reversed the polarity of the Optos when they went to the G203. Especially since most of the circuits/ports used for driving the inputs are capable of sinking much more current than they can source.

[vladdy]

I agree that most ports will sink more current as opposed to source..
In _my_ personal preference I source from the pc for control signals and sink at the pc for status lines [limit switch, stop, etc..] mainly for safety..if something goes wrong and a wire gets cut, or shorted, in most cases this arrangement _should_ be safer. less chance of erroneous signal generation or cases of running past limits, or no emergency stop signal..
as far as the 203v requiring pc source, I have no idea why they did it that way, but I liked it enough to order a couple of them to upgrade my old home made plasma table, they just came in yesterday late afternoon, and I [hopefully] will get them installed by this weekend..

[phomann]

The subject was discussed on the geckodrive yahoo group when the design of the G203 was being discussed.

If memory serves me correctly, the new optocircuitry used in the G203V was able to be driven from the 3.3V voltage from the new printer ports, therefore allowing for either active lo or active hi input.

after everyone put there case forward it was decided to use the active hi logic. I can't recall the justification for it though.

Cheers,

Peter.

Originally Posted by Clockwork I have both G201 and G203V drives. It's been bugging me why Gecko reversed the polarity of the Optos when they went to the G203. Especially since most of the circuits/ports used for driving the inputs are capable of sinking much more current than they can source.

[Mariss Freimanis]

Easy enough to reiterate the reasons.:-)

1) Current sinking requires COMMON to have a + voltage. That voltage is most usually 5VDC from a PC. A parallel port logic '1' nowadays is 3.3V and it cannot be pulled-up higher than 3.3V. 5VDC on COMMON and 3.3VDC on STEP leaves 1.7VDC across the optoisolator LED and the LED never turns completely off. This means the input can only work with 5V logic signals.

2) Current sourcing requires ground on COMMON. The STEP input then works with 1.8V, 2.5V, 3.3V and 5V logic level signals. The G203V needs only 2.5mA LED current to operate, so driver current sourcing is not so important anymore.

3) It's a pain in the posterior to find 5VDC on the back of a PC while ground is readily available. Accidentally shorting the PC 5VDC to ground can cause major PC problems. These are not possible when COMMON is ground.

Mariss

[phomann]

See, I knew there were good reasons, I just couldn't remember. :-)

Cheers,

Peter

Originally Posted by Mariss Freimanis Easy enough to reiterate the reasons.:-) 1) Current sinking requires COMMON to have a + voltage. That voltage is most usually 5VDC from a PC. A parallel port logic '1' nowadays is 3.3V and it cannot be pulled-up higher than 3.3V. 5VDC on COMMON and 3.3VDC on STEP leaves 1.7VDC across the optoisolator LED and the LED never turns completely off. This means the input can only work with 5V logic signals. 2) Current sourcing requires ground on COMMON. The STEP input then works with 1.8V, 2.5V, 3.3V and 5V logic level signals. The G203V needs only 2.5mA LED current to operate, so driver current sourcing is not so important anymore. 3) It's a pain in the posterior to find 5VDC on the back of a PC while ground is readily available. Accidentally shorting the PC 5VDC to ground can cause major PC problems. These are not possible when COMMON is ground. Mariss

[digital_life]

Originally Posted by Mariss Freimanis Easy enough to reiterate the reasons.:-) 1) Current sinking requires COMMON to have a + voltage. That voltage is most usually 5VDC from a PC. A parallel port logic '1' nowadays is 3.3V and it cannot be pulled-up higher than 3.3V. 5VDC on COMMON and 3.3VDC on STEP leaves 1.7VDC across the optoisolator LED and the LED never turns completely off. This means the input can only work with 5V logic signals. 2) Current sourcing requires ground on COMMON. The STEP input then works with 1.8V, 2.5V, 3.3V and 5V logic level signals. The G203V needs only 2.5mA LED current to operate, so driver current sourcing is not so important anymore. 3) It's a pain in the posterior to find 5VDC on the back of a PC while ground is readily available. Accidentally shorting the PC 5VDC to ground can cause major PC problems. These are not possible when COMMON is ground. Mariss

i need a little help..you may have the answer. i have a handheld Dsp wich uses 5Vdc as common but my drives (servo drive) needs to see 0V as common. is there any simple circuit i can make to resolve this issue?
thanks in advance!