TTL I/O IC buffer ot coupler ?

grasshopper

Is there a good method or an ic that i can use with my propeller that will buffer/couple my circuit with another. I was thinking about a optoisolator or a transistor but i would like an ic with many i/o pins. I cant seem to find one.

Mike Green

There are hundreds of different optocouplers and buffers available. You'll have to give more detail about your circuits and what sort of signals you want to couple and how much isolation you need, etc.

grasshopper

well to be more specific.

I want to be able to receive a command from a computer that my propeller will look up on a table. Afterwards it can toggle an output [noparse][[/noparse] high(5V) or low(0V) ] to turn on a device that accepts a TTL signal. The same idea should work in return to the propeller from the device as well. here is a picture...

Mike Green

At the top of this forum's thread list, there's one called "Propeller Hardware stickies (Voltage translation and Example hardware diagrams)". This is full of discussion, examples, circuit diagrams, etc. on just this issue. Please read it.

Generally, if you use a 1K resistor in series with the input pin, the Propeller can handle 5V logic inputs itself. The "sticky" thread goes into detail on why that's so.

5V logic outputs are much the same. Most 5V TTL device inputs will work just fine with the 3.3V outputs of the Propeller. The switching threshold for TTL is 2V or less for most devices and the Propeller will supply 3V or better to most TTL inputs. It's usually safer to provide some kind of series resistor even on an output and 220 or 330 Ohms will work.

Again, read the "sticky" thread because there are lots of other solutions to this depending on the details of your circumstances.

grasshopper

Thanks again Mike I read the sticky you mentioned. Perhaps some day I will be of assistance to you. Again thanks