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Topic: How to connect a 5v TTL board to Due (Read 1 time) previous topic - next topic

KurtE

Feb 09, 2013, 11:09 pm Last Edit: Feb 10, 2013, 03:04 am by KurtE Reason: 1
I am sorry if this has been answered before, but my searches are not showing up any thing...

I would like to connect one of the USARTS of the DUE to an SSC-32 (servo driver board), whose TTL is at 5v.

What is the preferred way to connect them.  I figure the TX is fine as the SSC-32 will probably handle the lower voltage just fine.  But about the RX where the SSC-32 may return data.

Limiting Resistor? if so how big

Resister Divider?

Other?

Thanks
Kurt

retrolefty


I am sorry if this has been answered before, but my searches are not showing up any thing...

I would like to connect one of the USARTS of the DUE to an SSC-32 (servo driver board), whose TTL is at 5v.

What is the preferred way to connect them.  I figure the TX is fine as the SSC-32 will probably handle the lower voltage just fine.  But about the RX where the SSC-32 may return data.

Limiting Resistor? if so how big

Resister Bridge?

Other?

Thanks
Kurt


A simple two series connected resistor voltage divider is probably the easiest solution if you just need it for one or few Due input pins. There are many 'voltage translator' ICs available also.

Lefty

bobcousins


I am sorry if this has been answered before, but my searches are not showing up any thing...

I would like to connect one of the USARTS of the DUE to an SSC-32 (servo driver board), whose TTL is at 5v.

What is the preferred way to connect them.  I figure the TX is fine as the SSC-32 will probably handle the lower voltage just fine.  But about the RX where the SSC-32 may return data.

Limiting Resistor? if so how big

Resister Divider?

Other?


If you are planning to connect to the DB9 connector you need to handle voltages -12 to +12. TX might possible work at 3.3V, but it is pretty borderline. I would use something like MAX3223 to provide proper translation levels.
Please don't PM me asking for help. Ask questions in the forum.

KurtE

#3
Feb 10, 2013, 04:02 pm Last Edit: Feb 10, 2013, 04:14 pm by KurtE Reason: 1
Thanks, the SSC-32 can be hooked up through RS232 signals, which I would then use a Max232 or the like to hook it up.  However it is also set up to use TTL level inputs/outputs, which I normally use when connecting up to a micro-controller.

I have dealt a little with the 3.3v to 5v issue a few times now, with a few different platforms especially with connecting up XBee's to controllers.  I am a software persons, so please pardon if I get a few terms slightly off...  Some approaches I have used in the past include:

a-) Pic32. - Just wired them up.  Most of their IOs are 5v tolerant.

a) Current limiting resistor.  I believe that this was all that was necessary hooking up a propeller to the SSC-32.  I believe they have clamping diodes or the like protecting the propeller...

a+) Diode(s)? Never used this approach

b) Resistor Divider from the TX of the SSC-32 to the RX of controller. Assume that the 3.3 output from DUE will be high enough for a high on SSC-32... Note: I have run into issues with XBees on Sparkfun XBee converter...

c) like b) but with mosfet transister and 2 resister level shifter circuit - What I have used for XBees on the shield...
(http://husstechlabs.com/support/tutorials/bi-directional-level-shifter/)

d) Use a level shifter IC like: TXB0108 there is also a 4 channel version s well.  I believe this is what Parallax uses on their XBee interface boards which have always worked well for me.  Also Adafruit sells a simple breakout board for them: http://www.adafruit.com/products/395

I am thinking I probably should do c) or d), but was wondering what others have done.

Thanks again
Kurt


bobcousins

Well, I think there is no general answer. Even in this specific case, it depends on what drivers the SSC-32 has. I suspect you know more about that than we do, but you haven't told us what chip it uses; looking at it's schematic is the only way to find out what will work. An answer also depends on what switching rate, how many channels, is it bidirectional, open drain, TTL/CMOS, TH/SMT etc. Just too many unknowns which only you can decide.

There are dozens of ICs available depending on requirements, I would try to use one of those, particularly if unidirectional.

I think you are aware of the possible solutions, but only you can decide what is best for your application.
Please don't PM me asking for help. Ask questions in the forum.

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