Sharing TTL Signal - Multiport option - Page 1
Forum section: electronics / beginners

author: gjh
author_rank: Contributor
timestamp: June 18, 2012, 01:06:33 am
content: Need some help to be pointed in the right direction.. Say I had a standard MAX3232 TTL -> RS232 circuit... Everything is v5 supply/signalling..How can I add a FTDI232 driver and all-in-one v3.3 bluetooth module to broadcast across all port options simultaneously? ie. simple sensor data sent out on RS232 port, USB Port, Bluetooth all at the same time..Was playing around with the following ideas -1/ Convert whole circuit to 3.3v supply/signalling to keep bluetooth module happy and to lower complexity perhaps.2/ Keep circuit at 5v standard, and lower supply/signally just before bluetooth module.3/ Share TTL signal perhaps using transistor switching..4/ Add FTDI232 driver behind MAX3232, sharing TTL signal with T1/T2 & R1/R2 if option 3/ is no good.5/ In the end it might be simplier just to add a switch to change switch between output method since each switch position would have its own independent circuitry where I can switch the TTL signal to.The sparkfun 5v <-> 3.3 TTL signal convertor has caught my eye, but not sure about the most elegant approach..

author: ejeffrey
author_rank: Super Contributor
timestamp: June 18, 2012, 04:47:17 pm
content: If you have the ability to respin I would just convert the whole circuit to 3.3 volt and connect all the transmitters in parallel. If not, I would use a level translator for the bluetooth module -- you can buy commercial ones, or hack something simple up. RS232 is slow enough you could use a simple voltage divider if you wanted.You can broadcast transmit but not receive, so if you need 2 way communication you will need three separate serial ports, or you need to switch between them.

author: gjh
author_rank: Contributor
timestamp: June 19, 2012, 01:20:50 am
content: I was thinking of using a FET to convert logic from 5v to 3.3v.. I probably prefer not to use another IC.ie..http://www.rocketnumbernine.com/2009/04/10/5v-33v-bidirectional-level-converterI've already have a voltage divider for the MAX3232 for T1-IN and using Transister switch on R1-OUT.. I dont think i can wire up other drivers straight in parallel I'll probably need some sort of transister switching I guess.. really fuzzy about that part.I've already tried wiring in MS3232 with FTDI232 directly in parallel since they both accept 5v logic and doesnt work so probably vdrop or something.. still learning, so in trial and error stage of learning different ways of implementing but having fun at the same timeMany thanks for your response ejeffrey, I really appreciate it!

author: digsys
author_rank: Unknown
timestamp: June 19, 2012, 01:49:36 am
content: I'd be extremely surprised if ANY 3V3 RS232 chip wasn't completely tolerant to 5V in/out ANDthat ANY 5V RS232 chip couldn't handle 3V3 signals. In fact, MOST should have no issue with+-12V PLUS. On the logic side, there are many 3V3 series that handle 5V without issue, andvise versa. You should NOT need to do voltage translation. I do these interfaces all the time.I recently needed a very similar IF, so I simply created the "Network" part on the TTL side,MUCH easier. The circuit also includes CTS/RTS or DTR/DSR busy/in use option.

author: gjh
author_rank: Contributor
timestamp: June 19, 2012, 04:46:12 am
content: Thanks for the diagram Digsys!Normally I just stick with simple one type of interface designs, but I really want to expand my horizons..I've found basically two different schematics which covers what I want to do... one has a UART TTL to rs232 & USB and the other has UART TTL to rs232 & Bluetooth using the same module I have HC-05..So I just need to understand the schematics (ie. use of buffers and transistor switching) and put together a UART TTL to rs232/usb/bluetooth interface. Only the all-in-one bluetooth module isn't 5v tolerant.. I guess I'll experiment in stages and try different setups to learn more.