Microcontrollers Networking

[dknguyen]

Has anyone experience with differential drivers/receivers? Trouble is you need differential voltages - unless you invert the bits +/- then -/+ on the wires, rather than reference to ground.

Do you mean bipolar voltages (as in +/-5V)? If so, you are mistaken. Differential voltages do not have to be centered around 0V. In fact, RS-232 is centered around 0V and it is NOT differential (for example, <-6V being a HI and >+6V being a LO), while RS-485 is differential and is centered around a positive voltage (for example if the common mode voltage/center/bias between the two differential lines happened to be 1.5V, a differential voltage of less than 0.4V (ie. <1.7V and >1.3V on the lines) being one logic state, and a voltage differential of greater than 1V (ie. >2V and <0.5V on the two lines) being the other logic state.

Differential simply means that rather than the lines using ground as their reference, they are using each other as their reference with no implication to the polarity of the voltages used.

NOTE: These voltages are for illustrative purposes only and may not be the actual thresholds used.

 

[WardXmodem]

Thanks! I guess I just was wondering if I could "cheat" = low parts count, using say 2 lines of a PIC output, driving A hi and B low, and A and B are my output lines. Then drive A low and B high, and thus flipping polarity, ....

wait, that's not differential.

I guess I think of traditional signals as being like the on-board - reference to ground, and say TTL being +5 and ground.

I think of differential as the 2 output lines having NO ground reference, and being driven "apart" (say 0v and anything - say 5v). Thus +2.5 -2.5.

I guess I could have TTL differential output by having say one output line is tied to pin A, which is tristated and pulled up/down by 1K's. Thus it puts out 2.5, and when you want, you un-tri-state the pin to say +5, or 0, while the "B" pin, similarly held at 2.5V with a pair of 1K's (not a very strong signal since 1K can be overcome easily) is then pulled to the opposite voltage, producing an opposite - though always positive WRT Ground - voltage. ..

BOY would it be neat to be building a house, and being able to run LV wiring / extra twisted pair signal cables "all over the place", heck, I keep thinking - have for years - you have FIBER/FIBRE running everywhere, if there was an easy way to "insert nodes".

Some of the "highly wired" or "home of the future" seem to put sensors on "everything" like every door, light, etc. Wonder if they hard wire all those? Oh, those are probably rich people and they can afford a wireless chip at every node? It would just have to transmit on state change, then go back to sleep, perhaps waking once an hour to "check in" for a health check, or "my batt is dying", etc.

Thank you all for the wonderful replies. I posted some msgs in other places - simple MOSFET question, and got no answers in 1.5 yrs. ;-)