How to wire output on one device to input on another device

[PaulKraemer]

Hi

I have a device (#1) that has a digital input. In order to put thi
input in the "ON" state, you have to connect the input pin the th
ground pin on the device

I have another device (#2) that has a digital output. It is describe
as an open-collector MOSFET output rated for up to 170 mA and 40Vdc.
According to the manual, an "on" condition is a 5-ohm resistance t
ground. An "off" condition is an open-circuit.

I want to wire the output on device #2 to the input on device #1. Ca
anyone tell me how I can do this and if I need any additional part
besides wire

Thank you
Pau

 

[Chris]

Hi,

I have a device (#1) that has a digital input. In order to put this
input in the "ON" state, you have to connect the input pin the the
ground pin on the device.

I have another device (#2) that has a digital output. It is described
as an open-collector MOSFET output rated for up to 170 mA and 40Vdc.
According to the manual, an "on" condition is a 5-ohm resistance to
ground. An "off" condition is an open-circuit.

I want to wire the output on device #2 to the input on device #1. Can
anyone tell me how I can do this and if I need any additional parts
besides wire.

Thank you,
Paul

Hi, Paul. It's easy. Open-drain outputs can be treated just like
open-collector outputs. You just need a pullup resistor to the logic
power supply.

Assuming you have that power supply available, wire up something like
this (view in fixed font or Notepad):


.---------------. .----------------.
| Device #1 | ___ | Device #2 |
| Vcc o-|___|--. | |
| | 1K | | |
| | | | Open Drain |
| | | | Output |
| In o--------o------o |
| | | |
| | | |
| | | |
| | | |
| Common/GND o---------------o Common/GND |
| | | |
'---------------' '----------------'
created by Andy´s ASCII-Circuit v1.24.140803 Beta www.tech-chat.de

Note that the MOSFET will do the exact same thing as connecting the In
on Device #1 to GND. The pullup resistor may not be necessary, because
Device #1 may have an internal pullup resistor to keep the In at a
logic "1" when not active. Or it may have a TTL input which goes to a
logic "1" when left floating. But an external pullup is usually used,
and probably won't hurt.

This is a best guess based on the information you've provided. It
should work, but you really should contact the manufacturer or read the
manual on the devices, or provide more information.

Good luck
Chris

 

[John Popelish]

Hi,

I have a device (#1) that has a digital input. In order to put this
input in the "ON" state, you have to connect the input pin the the
ground pin on the device.

That is called an "active low" input.

I have another device (#2) that has a digital output. It is described
as an open-collector MOSFET output rated for up to 170 mA and 40Vdc.
According to the manual, an "on" condition is a 5-ohm resistance to
ground. An "off" condition is an open-circuit.

That is an "active low" output intended to drive loads connected
between it and a positive supply.

I want to wire the output on device #2 to the input on device #1. Can
anyone tell me how I can do this and if I need any additional parts
besides wire.

Assuming there is no problem connecting the two system grounds
together, you do that, tie the output to the input and add a pull up
resistor to that line (say, 4.7 k ohms to a + 5 volt supply) so that
when the output goes open circuit, there is something to make the
input voltage positive. The pull up resistor may already be connected
to the input, internally. Check the input voltage to its common, with
nothing else connected. If it is near 5 volts, then this is the case.

 

[PaulKraemer]

Chris & John,

Thanks for your responses, you've been a huge help. Both of yo
mentioned that my input might have an internal pull-up resistor. I
does. Here is the description from the manual..."each input has
4.7K pull-up resistor and is protected for input voltages up to 3
Vdc. Inputs are compatible with CMOS and TTL logic operating from 5
supplies, with other pump's digital outputs, and with externa
switches. An "on" input is less than 1V. An "off"input is more tha
3.5 V, or an open circuit. The internal resistance provides the bia
for required external switches. External switches should make
connection to ground when in the "on" condition.

I think I understand John's response and I can figure out how to wir
this. I assume that there is no problem connecting the system groun
because device #1 and device #2 are actually just two of the sam
device (syringe pumps). It looks like I don't have to add a pull-u
resistor myself, so it sounds kind of easy. Of course, I'll run i
by the manufacturer before I connect the wires, but I am just tryin
to see if I can learn a little

Chris, I had a hard time following your schematic. I copied it fro
this forum and pasted it into notepad, but the columns didn't seem t
line up right. If you have any suggestions, or if you could possibl
email it to me as a .txt file at [email protected] (jus
remove the NOSPAM), I would really appreciate it. If you coul
remove the pull-up resistor if you don't think I need to add it, tha
would be great too

Thanks again to both of you
Pau

 

[Chris]

Chris & John,

Thanks for your responses, you've been a huge help. Both of you
mentioned that my input might have an internal pull-up resistor. It
does. Here is the description from the manual..."each input has a
4.7K pull-up resistor and is protected for input voltages up to 30
Vdc. Inputs are compatible with CMOS and TTL logic operating from 5V
supplies, with other pump's digital outputs, and with external
switches. An "on" input is less than 1V. An "off"input is more than
3.5 V, or an open circuit. The internal resistance provides the bias
for required external switches. External switches should make a
connection to ground when in the "on" condition.

I think I understand John's response and I can figure out how to wire
this. I assume that there is no problem connecting the system ground
because device #1 and device #2 are actually just two of the same
device (syringe pumps). It looks like I don't have to add a pull-up
resistor myself, so it sounds kind of easy. Of course, I'll run it
by the manufacturer before I connect the wires, but I am just trying
to see if I can learn a little.

Chris, I had a hard time following your schematic. I copied it from
this forum and pasted it into notepad, but the columns didn't seem to
line up right. If you have any suggestions, or if you could possibly
email it to me as a .txt file at [email protected] (just
remove the NOSPAM), I would really appreciate it. If you could
remove the pull-up resistor if you don't think I need to add it, that
would be great too.

Thanks again to both of you,
Paul

Hi, Paul. It's not much of a schematic -- it basically suggests pretty
much what John was saying, connecting GNDs or Commons together,
connecting the innie of Dev1 to the Outie of Dev2, and use an external
1K pullup resistor from the logic power supply of Dev1 to the innie of
Dev1.

ASCII circuits with a lot of whitespace sometimes don't copy well in
some newsgroups. Sorry for that.

As long as the two devices are close to each other and it's not an
electrically noisy environment, you shouldn't have any problems with no
pullup resistor. If you have a problem with false triggering, you
might want to add an external pullup.

Good luck
Chris

 

[Jamie]

Hi,

I have a device (#1) that has a digital input. In order to put this
input in the "ON" state, you have to connect the input pin the the
ground pin on the device.

I have another device (#2) that has a digital output. It is described
as an open-collector MOSFET output rated for up to 170 mA and 40Vdc.
According to the manual, an "on" condition is a 5-ohm resistance to
ground. An "off" condition is an open-circuit.

I want to wire the output on device #2 to the input on device #1. Can
anyone tell me how I can do this and if I need any additional parts
besides wire.

Thank you,
Paul

just connect the output of device #2 to the input of Deivce #1.

the open collector mode is simply pulling what ever you connect
to it to ground/common

 

[Rich Grise]

Hi, Paul. It's not much of a schematic -- it basically suggests pretty
much what John was saying, connecting GNDs or Commons together,
connecting the innie of Dev1 to the Outie of Dev2, and use an external
1K pullup resistor from the logic power supply of Dev1 to the innie of
Dev1.

ASCII circuits with a lot of whitespace sometimes don't copy well in
some newsgroups. Sorry for that.

As long as the two devices are close to each other and it's not an
electrically noisy environment, you shouldn't have any problems with no
pullup resistor. If you have a problem with false triggering, you
might want to add an external pullup.

If they're more than a foot or so apart, you might want to use a
"twisted pair" - two wires twisted together, to minimize noise
pickup, but here's your schematic: (I've used '_' to take up space,
in case you're reading by google or haven't yet figured out how to
set your newsreader's font to 'Courier')

Output from device 1 o--------o Input to device 2
__ Ground of device 1 o--------o Ground of device 2

You might have to swap "1" for "2" in the above - I don't remember
which you were connecting to which, but it's the same connection
in either case, so no worries.

In Other Words, two wires, and you're good to go.

Cheers!
Rich

 

[JeffM]

Chris, I had a hard time following your schematic

...the columns didn't seem to line up right.
PaulKraemer

http://groups-beta.google.com/group/sci.electronics.basics/msg/89cc94351d013635?dmode=source

 

[PaulKraemer]

thank you Chris for emailing me the diagram, and to jeff for providin
the link. I can read it now and I'm ready to connect my device
together. You have all been very helpfu