Sending power over data, 24 volt Dc communication

Thread Starter

Kathode

Joined Jun 19, 2020
2
How, can i send data through power supply cable( 24 Volt DC) for communicating between 2 microcontrollers ?

Tried with rs 232, manchester encoding, In transmitter side, with capacitor coupling to power supply and inductor to avoid flow of signals to power supply.

Receiver side also, capacitor coupling used with inductor to decode Manchester encoded data with microcontroller.

Found approach not working.Where i am wrong in this appproach.
 

DickCappels

Joined Aug 21, 2008
6,459
This system was designed to supply 12 volts to the remote device, but it might give you some ideas of how to do it for 24 volt out.


1592661434798.png

When its not worth the expense and hassle of Ethernet, these adapters use a combination of tricks so that a single pair of wires carries full duplex serial data and a small amount of power to a remote device for tasks such as continuous remote data collection and control. The digital signals can be simple on/off signals as well as more complex signals such as RS-232.


1592661465996.png

The Base Adapter includes a 15 volt power converter so that the adapter can be powered from a 5 volt Universal Serial Bus cell phone charger. Optionally, +15 volts can be supplied directly, eliminating the need for the +5 volt to +15 volt converter.

1592663079708.png
Data from the base adapter are sent by level shifting the RS-232 or CMOS serial data between 9 volts and 12 volts. A voltage comparator at the remote adapter slices the signal to generate a 0 to 5 volt logic signal. The voltage on the signal wire is always sufficient for the 5 volt regulator to remain in regulation.


1592663094159.png
The data flows from the remote adapter (right) to the base adapter (left). Steady current is drawn by the shunt regulator and serial data is added to the regulator current with a switched current source.

1592663194715.png
The base unit including the 5 volt to 15 volt power supply is still very simple for its functionality. The two 8 pin Dual Inline Package Integrated Circuits are a voltage comparator and the switching regulator.


The 5 volt to 15 volt power supply requires care in routing the grounds. High peak currents flow between the negative end2 of C51 and the C53, and the negative end of C51 and U1 pin 2.

1592663224981.png
Three terminal voltage regulator U3 provides 12 volts while Q3 switches between the states of passing the 12 volts or dropping it down to 9 volts as a function of the state of the signal from the terminal.

Automatic Polarity Switch
1592662010556.png

If, during installation, the signal and return lines happen to be switched at the remote adapter, nothing will work and the base unit's current limit capability will be tested -its not good to tempt the fates! It also might be inconvenient to diagnose and correct the error, particularly given that the two ends of the system may be separated by over 100 meters of wire. A very low forward-drop full wave bridge built into the remote adapter would solve that problem. Schottky diodes can do the job, but they leave very little "headroom voltage" to allow for very much of a voltage drop on the line and return conductors. Using an automatic active switch using low on-resistance Metal Oxide Field Effect Transistors like the one in Figure 6 can do a really good job directing the signals from the signal and return lines to the correct inputs on the remote adapter power supply and transceiver circuit.

The P-Channel and N-Channel Metal Oxide Field Effect Transistors inside the FDS8958A Dual Metal Oxide Field Effect Transistor have a total series resistance of less than 80 milliohms. With the maximum current drain of 35 milliamps. the maximum voltage drop across the bridge of only a few millivolts. That's a nice switch and the voltage drop should not have a significant effect on the operating capabilities of the system.

The Metal Oxide Field Effect Transistors are rated at only 20 volts between the gate and drain, so 15 volt Zener diodes were adde to prevent any two external connections from having a voltage difference of more than 30 volts. Besides protecting the MOSFET gates, it also provides some protection against induced transients for the rest of the system.

1592663276045.png
The remote adapter is very simple and requires very little board space.

Result:
Using what I have on hand, I have tested this with 120 meters of a combination of #23 telephone wire, 0.5 mm square lamp cord and 50 ohm coax. With the 0.1 microfarad low pass filter shown for C5 reliable full duplex communications were observed at 38,400 baud. My application of communicating with a single chip computer via terminal requires 9600 baud so it should be good for a much longer run for my use if ever needed.

If more detail is desired you may pm me for a URL for this project.
 
Top