Design Advice

[isaac]

. Have a wand in the cab for the driver, when he gets out, he touches the I-Button on the trailer that transfers the trailer info to the wand. Driver hooks up the trailer, gets back in the cab, LCD displays the trailer info for the driver. The wand part is already a product. Our guard at work has one, there are check points through out the building. Once he's back to the office, he sets the wand in the cradle and it downloads all of the checkpoints. Kind of a check on the guard to make sure he's making the rounds. Just another idea.

What is a wand?

Regards
Isaac

[isaac]

Thanks everyone
i have learnt a lot from you all and gone back to him
i emailed him that it has to be wireless modules or the barcode idea its up to him now.

Thanks again for your contributions

Isaac

[rhino]

What is a wand?
Regards
Isaac

I was thinking you could duplicate something like THIS. You can purchase a simple probe HERE. This would make the unit portable, but would require the driver to remember to scan the trailer when it gets hooked up...... I say scan, but what I really mean is take the probe/wand and touch the I-Button on the trailer to get the information off of it.

[isaac]

Hi All

I have just got an email from the customer he likes the idea of using an ibutton (Doesn't want wireless?)but he still insist that he does not want the driver to get out of the cab to touch the ibutton so i am nearly back to square one.(He wants to use the line for the revease line.
i was thinking i was thinking of using an ibutton but i need to isolate the 24v that is put on the line when its in reverse somehow.
i also dont know if the 1 wire protocol can withstand noise etc.
i need some guildance on this.
i attached the schematic which i would like to use but not quite sure if this would do the job

Regards
Isaac

[Darrel Taylor]

For iButtons, you have to have a Pull-up resistor that supplies both power and the high side of the data.

I don't think the pull-up can overcome the Pull-down from the filaments of the light bulbs.
And if it could, the lights would always be partially on, and the ibutton would be dead after the first pulse trying to drive that much current.

Due to the inductance of the filaments you might be able to pass a low freq RF over that line, but probably not DC.
<br>

[isaac]

Ooops
it back to the drawing boards

[isaac]

For iButtons, you have to have a Pull-up resistor that supplies both power and the high side of the data.

I don't think the pull-up can overcome the Pull-down from the filaments of the light bulbs.
And if it could, the lights would always be partially on, and the ibutton would be dead after the first pulse trying to drive that much current.
<br>

Yes i agree with you i didn't take this into consideration

Due to the inductance of the filaments you might be able to pass a low freq RF over that line, but probably not DC.
<br>

How can i do this i am cracking up here

Regards
Isaac

[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.
<br>

[rhino]

Due to the inductance of the filaments you might be able to pass a low freq RF over that line, but probably not DC.
<br>

This sounds like a cool idea..... like X10?