Simplest way to send a control signal down a DC power line?

[4pyros]

I what to use 30 or so microcontrollers as timers all hooked up to the same 24 VDC power line spaced 30 or so feet apart in one continuous chain. To control what we call a mine run. I want them all to have power all the time and wait for a signal to start a user selectible time delay. The 1st one will get a signal from a firring sytem, wait .05 to 1 sec. and send a signal to the next timer to start and so on.
I am thinking of using a form of a bias tee. With inductors passing DC down the line and isolating the control signal, but I am not shur of the best way to couple a signal to and from the microcontroller to the DC line. Can I just use a cap from the DC line to a microcontroller pin? Will I need a transister to drive it? Will I need to use a transformer?
Any thoughts on this holiday break?
Is thare a better way?
Marry Christmas.
Andy

 

[Diver300]

The transmitting device needs enough power to drive a large enough signal down the line. If you have inductors, then the transmitting device needs to be able to source enough current to give a detectable voltage across the parallel combination of all the inductors.

The current taken by each device will have a big effect on how physically large an inductor of a certain value is. Please tell us what sort of power you need.

A capacitor isolating the control signal is fine, but make sure that you have clamping diodes after the capacitor. You should also bias the signal after the capacitor either low or high so that when the transmitter is idle, the state of the receivers is known. All signals have to be brief enough that the inductors effectively block them, and so that the capacitors transmit them, although the inductors will be the problem.

You might look at adapting the Dallas 1-wire signalling system, where breaks in the power are the signals. Each node need a diode and a capacitor, and the capacitor has to keep the node going for the longest signal. However, the diodes go very high impedance when the wire voltage drops, so driving the wire is quite easy, and no capacitors are needed.

You can even do what Dallas do for items that need significant power. They need a break from signalling while power is needed, so that a strong pull-up is applied. That would reduce the size of the capacitors a lot, as the firing could just take power from the wire.

 

[4pyros]

The transmitting device needs enough power to drive a large enough signal down the line.

The signal would only need to go about 20 feet to the next timing node. I hope this fact can simplfy things.

 

[Nigel Goodwin]

I what to use 30 or so microcontrollers as timers all hooked up to the same 24 VDC power line spaced 30 or so feet apart in one continuous chain. To control what we call a mine run. I want them all to have power all the time and wait for a signal to start a user selectible time delay. The 1st one will get a signal from a firring sytem, wait .05 to 1 sec. and send a signal to the next timer to start and so on.
I am thinking of using a form of a bias tee. With inductors passing DC down the line and isolating the control signal, but I am not shur of the best way to couple a signal to and from the microcontroller to the DC line. Can I just use a cap from the DC line to a microcontroller pin? Will I need a transister to drive it? Will I need to use a transformer?
Any thoughts on this holiday break?
Is thare a better way?
Marry Christmas.
Andy

You didn't like the previous answers to your earlier thread?.

 

[alec_t]

It would simplify the timing nodes considerably if you could use a 3-core cable (2 cores for power and 1 for signalling). Is that an option?

 

[4pyros]

You didn't like the previous answers to your earlier thread?.

I am still thinking about it and brain storming. Trying to come up with the easyest way to signal the next timer using just the power wires.

 

[4pyros]

It would simplify the timing nodes considerably if you could use a 3-core cable (2 cores for power and 1 for signalling). Is that an option?

Trying to avoide this but it may be the best way.

 

[picbits]

Use a variable voltage regulator for the drive to all the units.

Set it to say 10 volts when there is no signal and 15 volts when you want to signal via bias resistors switched in or out by a transistor at the master end.

Each slave can have its own onboard voltage regulator and comparator. When the slave sees 15 volts it can time the interval. <100ms for example is a zero, >100ms but less than 500ms is a 1 and >500ms is a reset signal.

Obviously play with timings and voltage to suit your application.

 

[rogs]

Use a bridge rectifier to power each node, and simply reverse the polarity of the supply line, to indicate the signal state, and detect that polarity using an extra diode at each node.

Edit - sorry just read original post again. If I understand, every node has to provide enough transmitted 'power' to signal the next node only.....
Interesting challenge with 2 wires......

 

[4pyros]

Use a variable voltage regulator for the drive to all the units.

Set it to say 10 volts when there is no signal and 15 volts when you want to signal via bias resistors switched in or out by a transistor at the master end.

Each slave can have its own onboard voltage regulator and comparator. When the slave sees 15 volts it can time the interval. <100ms for example is a zero, >100ms but less than 500ms is a 1 and >500ms is a reset signal.

Obviously play with timings and voltage to suit your application.

I was thinking along those lines before. Using two 12 volt batterys. Have all units powered up and waiting with 12 volts and then send 24 volts to fire. But I couldn't figure out how to isolate the 24 volts at each of the the nodes so thay dont all trigger at once.

 

[rogs]

OK, taking the reverse polarity concept one stage further. As the units are powered all the time, and you intend to adjust the timers on each one individually, why not simply make the 'start timer' delay adjustable as well. That way, the single 'reverse polarity' detect would simply start all the timers at once, with all the different delayed 'start' times as well as their preset 'on' times...

 

[4pyros]

That way, the single 'reverse polarity' detect would simply start all the timers at once, with all the different delayed 'start' times as well as their preset 'on' times...

The nodes will not be permanently connected. Thay will all be in one big box. So I am trying to make them all exactly the same exept for the 1st one witch will have a firring system interface and the batterys. That way there is no confusion during setup.

 

[rogs]

They will all be in one big box.

So why the 2 wire restriction then?........

 

[KeepItSimpleStupid]

Why don't you go three wire?

Have power, ground and signal. Make signal a half-duplex RS485 system.

What I might envision is that you "tell" each microcontroller what the delay is.
Have an ARM, FIRE, ABORT, ACK and NAK signals.
So, you would preload each timer with the delay and get a confirm back from the timer.
While this might require a laptop you could create a processor just for the load sequence and have 3 buttons, LOAD, ARM, Start, Abort and a few lights. Each delay would then be relative to the start pulse and not each other.

But 32 nodes is a problem and the distance is a problem. https://www.rs485.com/pfaq.html

Or, basically modulate the power supply rail with 2 tones for the arm sequence. Use a DTMF (2 tones) decoder to detect the start sequence. This means power electronics at each node and you have to manually set each timer.

 

[tytower]

Detonators only have 2 wires?

 

[4pyros]

So why the 2 wire restriction then?........

Thats what we already have and use. Zip cord 16 gage.

 

[4pyros]

Why don't you go three wire?

Have power, ground and signal. Make signal a half-duplex RS485 system.

What I might envision is that you "tell" each microcontroller what the delay is.
Have an ARM, FIRE, ABORT, ACK and NAK signals.
So, you would preload each timer with the delay and get a confirm back from the timer.
While this might require a laptop you could create a processor just for the load sequence and have 3 buttons, LOAD, ARM, Start, Abort and a few lights. Each delay would then be relative to the start pulse and not each other.

But 32 nodes is a problem and the distance is a problem. https://www.rs485.com/pfaq.html

Or, basically modulate the power supply rail with 2 tones for the arm sequence. Use a DTMF (2 tones) decoder to detect the start sequence. This means power electronics at each node and you have to manually set each timer.

We dont want to drag any more equpment out to the field to do it, it must all run off one firing que.

 

[4pyros]

Detonators only have 2 wires?

Detonators are for blasting. We use igniters or "e-matches".

 

[ronsimpson]

I do not fully understand but......
Here is a way of getting each light to turn on after a delay. Sorry no micro.
When 24V is applies the light bulb turns on. Then after a RC delay power is sent on to the next stage. R1=R2 (1mega ohm?)

 

[Nigel Goodwin]

I am still thinking about it and brain storming. Trying to come up with the easyest way to signal the next timer using just the power wires.

Like I said in the other thread, a diode and capacitor to power the circuit, and switch the supply ON and OFF as serial data, feed that in to the PIC UART, and power the PIC via a diode and a capacitor - the capacitor charges during the positive pulses, and the diode stops it discharging. Each device is given it's own address, so you can individual address as many as you like down one pair of wires - although a single byte address for 256 is probably plenty.

In a similar way to I2C, leave the power/data line high when there's no data, so it keeps everything powered.

If required you could even make it two way, although that's probably not needed?.