Design Advice

[isaac]

Thanks DT

what if the circuit is modified as the attached image
using the relay contact to completely isolate the lamp from the circuit

Regards
Isaac

[Darrel Taylor]

I don't know Isaac,

It looks like the delay of the relay would still allow the iButton to take a pretty big 24V hit. I don't think the parasitic power cap in the ibutton could take too many of those.

Just thinking out loud here.

If on the cab side, the current to the reverse lights was monitored with a hall effect current sensor. And, on the trailer side a normally ON solid state relay or FET was placed in series with the light bulbs. Then the lights can be turned on and off (fast enough not to interfere with the lights being on) by a PIC sending serial data. The current sensor in the cab would pick up that signal easily for the receiving side.

Then every time you put it in reverse, the 24V will power up the PIC and it'll transmit what it's attached to. Same thing could be done with brake, turn signals or running lights.
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[Archangel]

Hi Issac,
Your customers trucks are using 6 pin connectors? There are 7 pin trailer connectors available for large vehicles: http://www.accessconnect.com/images/wiring_7pole.jpg Does he now use a 7 pin with a charge line ?

[ZOOM]

I don't know Isaac,


Just thinking out loud here.

If on the cab side, the current to the reverse lights was monitored with a hall effect current sensor. And, on the trailer side a normally ON solid state relay or FET was placed in series with the light bulbs. Then the lights can be turned on and off (fast enough not to interfere with the lights being on) by a PIC sending serial data. The current sensor in the cab would pick up that signal easily for the receiving side.

Then every time you put it in reverse, the 24V will power up the PIC and it'll transmit what it's attached to. Same thing could be done with brake, turn signals or running lights.
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DT
How can this be posible as the pic in the trailer to send serial data (There is only going to be the 24v line as its output.

[Darrel Taylor]

The idea is to read the Current being sent to the reverse lights from the cab. It's actually an analog output from the current sensor, but with the sensitivity cranked up ... the output will be "High" (output saturated) with any current being drawn, and "Low" when there's no current.

Then in the trailer, it turns the lights on/off via serial data to the solid state relay.

For incandescent lights, fast on/off times won't be noticed visually. May cause a little dimming, but it only takes a few milliseconds to send the data so noone will even notice.

This way it doesn't matter what the voltage is on the line. Works on 12v just as well as 24V.

[ZOOM]

The idea is to read the Current being sent to the reverse lights from the cab. It's actually an analog output from the current sensor, but with the sensitivity cranked up ... the output will be "High" (output saturated) with any current being drawn, and "Low" when there's no current.

DT good explanation just like a squarewave

Then in the trailer, it turns the lights on/off via serial data to the solid state relay.

How are you going to feed this output back to the tralier as if i followed this tread correctly i think it was mentioned that the only connection between the trailer and the cab is going to be the 24V line ?

[Darrel Taylor]

How are you going to feed this output back to the tralier as if i followed this tread correctly i think it was mentioned that the only connection between the trailer and the cab is going to be the 24V line ?

There's no output from the cab to the trailer. Only the power being applied to turn on the Reverse(back-up) lights.

When the reverse lights are turned on, it powers a PIC in the trailer that's been pre-programmed with the trailers information in EEPROM (no iButton). That pic modulates the lights, which sends the data to the cab (via current) without the need for any additional wires.

The information would be sent only once or twice when the reverse lights are first turned on. Which is why I mentioned it could be done with the brake or turn signal too. Those will happen more frequently, and the Brake is guaranteed to happen when driving. Turn signals are not guaranteed, depends on the driver, but they're more likely than reverse lights.

[ZOOM]

When the reverse lights are turned on, it powers a PIC in the trailer that's been pre-programmed with the trailers information in EEPROM (no iButton). That pic modulates the lights, which sends the data to the cab (via current) without the need for any additional wires.

I see what you mean what a clever way to do this =)
But i still dont get it how the cab would be able to differentiate between two trailers
as with your earlier explaination

That pic modulates the lights, which sends the data to the cab (via current) without the need for any additional wires.

With the brake/Reserve pressed the input to the cab would be high all the time as the lamp is ON