Thank you for schematic Melanie ! You were right, I posted this question some months ago. You didn't understand my setup here. So, once again,
I have two devices ( not pics ). A master device, and a slave device that get power from the slave (5v, 3-400 mA ). Now, I want to put a PIC in the slave device which should send to the pic I put in the master device a few bytes ( 1200 baud ). The problem is the power consumption of the slave ( 4-500mA). And I can not use too big caps like ... 4700u@25v. I can not test the schematic right now, but I got the ideea. But do you thing it will work in the context I explained you ? The power on that slave device ( and the transmitting pic also ) should be kept as close as it can to 5V. Thank you .
If your Slave device is power hungry, then the only way is to modulate a signal onto the Power Supply lines as suggested by Keith. The schematic I've posted would not be appropriate in that instance.
I dont think you can even use the modulation technique in this instance because its the slave device he wants sending the data (i.e. the device that doesnt have a power supply).
You can use the mondulation technique if you were transmitting data from the master to the slave, but not slave to master.
If you already have 2 wires between the 2 devices, whats so hard about running a 3rd wire for data?
You got the point ! That's why I thought it might not work ! Although, someone did it, I don't know exactly how... Forget the 3rd wire...I just can not use more than 2 wires
No, it's irrelevant which end is supplying the power and which end is transmitting the data. Quickly, for example as I'm under pressure at the moment...
Slave is a 16F628 (building block of the modern world!). HPWM an output at say 40kHz... hardware cross-connect that back into one input of one of the on-board comparators. Take Hardware Serial out of USART or Software Serial out of any other pin. Hardware cross-connect that into your other Comparator Input. Take Hardware comparator output pin via Capacitor onto your Supply Line (yes, the supply will need a blocking choke). This will then transmit your modulated data signal back to the Master end. At the Master end, take via a Capaitor (PSU will need a blocking choke as well) into a demodulator (which if you chose the values correctly could be as simple as a Diode and a Capacitor), take it's output into USART or Software Serial pin. In it's raw basic form it's not exactly going to pass EMC specs but who cares anyway! It's not noise immune either, but repeat the data five times with a check-digit. Anyone with a problem with this concept, go read basic AM radio theory.
I dont think you can even use the modulation technique in this instance because its the slave device he wants sending the data (i.e. the device that doesnt have a power supply).
You can use the mondulation technique if you were transmitting data from the master to the slave, but not slave to master.
If you already have 2 wires between the 2 devices, whats so hard about running a 3rd wire for data?
I beg to differ.
The data would be used to turn on and off a carrier which would become an AC signal. This can be superimposed on top of a DC signal quite easily.
It doesnt matter which direction power or data are heading. They simply use the same piece of wire as their connection.
A phantom powered electret microphone effectively does what is requested here. Power is fed from the mixer (MASTER) whilst the audio (or Data) is fed along the exact same wires by the Microphone (SLAVE).
See attached diagram for how data and power would be connected. I havent draw the modulator and demodulator as I dont have a suitable design to hand but generating the signal could be as easy as running the PWM on the SLAVE PIC ad using a transistor driven the the TX data pin to modulate it. At the MASTER end you would need a circuit to detect the carrier and provide a logic level to drive the RX data pin on the Master Pic.
The inductors allow DC power to pass but block the AC carrier so that PSU compoments dont attenuate the carrier.
The capacitors allow the AC carrier to pass but block the DC supply voltage.
hm ... can you please be more specific ?
May I know the exact application
Originally Posted by Kamikaze47
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