I want to use a TRIAC as a switch to open a gate to transfer a 9600 baud rate square wave (for a uart communication between two avrs). Currently I'm using dc relay, but I'd like to use the Triac to reduce the power consumption and increase the components durability. But I'm not sure if the Triac will have any side effects.Please advice.Thx

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    \$\begingroup\$ Yes, a triac is hardly the component for the job. Please post your application circuit so we can suggest something better. Why do you even need to gate the transmission? Why aren't you using a logic gate? \$\endgroup\$ – HL-SDK Feb 11 '14 at 16:49
  • \$\begingroup\$ I have 3 avr MCUs,1 acts as server and 2 clients.They communicate using uart.The rx of the 2 clients going to the tx of the server and the tx of the clients going to the rx of the server.(this is my design and I don't know if there is a better way or a ready more component to better organize the communication). I found the connection to not work if the 2 clients are connected concurrently (possibly because when client1 communicates with the server, the 2nd will mess up the signal because it is sitting idle),so I put a relay to open the communication only when needed for each. \$\endgroup\$ – T Tuba Feb 11 '14 at 18:08
  • \$\begingroup\$ Hmmm, interesting configuration. Without trying to re-engineer your system, I'll try and write up an answer. \$\endgroup\$ – HL-SDK Feb 11 '14 at 18:17

Yes, I can think of a good alternative that is better than both a relay and a triac.

You seem to want to be able to select a unidirectional (slave to master) logic level bitstream.from 2 different sources. If you were to connect them together, you will get undefined results because of the output type (not open-drain).

You can use a number of different devices like transmission gates, discrete bipolars, and many other solutions but I suggest a digital switch (multiplexer/demultiplexer). Since you do not need linearity, these should exist in a standard logic catalog. Here are a few examples of analog multiplexers:

All of these options have multi-megahertz bandwidths so you should be good to at least 100kbaud

  • \$\begingroup\$ I actually did not answer the question because I do not know anything useful about triacs. \$\endgroup\$ – HL-SDK Feb 11 '14 at 18:36
  • \$\begingroup\$ My main concern is potential signal distortion of the triac. Do you think a simple AND gate will do with the swift on off? \$\endgroup\$ – T Tuba Feb 11 '14 at 18:50

I assume (hope?) that your communication protocol ensures that the two clients don't transmit at the same time. If that were there case, there would be no way for the master to receive the sum of what the slaves are transmitting.

When one slave UART is transmitting and the other is not you want your master to receive the transmitted signal. Idem when the other slave is transmitting.

A UART output in the idle situation is high. Hence you can combine the two UART signals using an AND port. The very common 74HC00 chip contains 4 NANDs. You could use one to combine the signals, one to invert the output back, and leave two unused (but tie their inputs to gound or power).

PS a TRIAC is NOT a good component in this situation. A bit like a power grinder is not the right tool for cutting a birthday cake.

  • \$\begingroup\$ so an AND gate ex. 7408 can handle the 9600 baud rate. what i understood from your analogy is that the triac should be used for bigger voltages/currentsCorrect? \$\endgroup\$ – T Tuba Feb 11 '14 at 19:01
  • \$\begingroup\$ @T Tuba That's right and Wouter good explanation. I also like the analogy >:D \$\endgroup\$ – HL-SDK Feb 11 '14 at 19:08
  • \$\begingroup\$ Thanks guys. I'll go with the AND gate since I have it in hand and they are inexpensive too. \$\endgroup\$ – T Tuba Feb 11 '14 at 19:13

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