The Great Wiring Conundrum

Brought to you by PCSensor

And Solution

Start by thinking back to the last Bad Day you had.

The nice people at PCSensor.com were busy building up a line of modules and sensors using chips from the Dallas 1-Wire family. They were all to be connected together with standard cables with 3.5mm plugs and sockets. PCSEnsor had a good "mix and match" scheme. There are diagrams on their web site.

If I have interpreted that information at their site correctly, the company's INTENDED "standard" is, and will be....

==== PCSensor's "standard".. the plan
From tip to base of plug...

Ground
1-Wire Data
V_cc

- - - - - And then there was a little boo-boo - - - - - - -

A few TEMPerLANs, sensors for them and some 1-Wire Relay modules went out wired as follows...

==== TEMPerLAN boo-boo...
From tip to base of plug...

V_cc
1-Wire Data
Ground

NOTA BENE: PLUGGING A TEMPerLAN WIRED SENSOR INTO A "STANDARD" WIRED ADAPTER WILL APPLY 5V ACROSS THE DEVICE "BACKWARDS". THIS SHOULD FRY IT.

Happily, modern semiconductors are remarkably forgiving, and I've got away with all sorts of things like that which I never should have... but you don't want to apply reverse voltage more often than you can help it! I think that some of my PCSensor DS18B20s survived some time plugged in backwards. I think my TEMPerLAN unit is okay after having sensors of the other sort plugged into it. I think that both a USB-1-Wire adapter and 1-Wire Relay unit are okay after being plugged into each other, when they had opposite wiring conventions.

Many of the other potential mis-matches of devices and sensors, etc, could also lead to Device Failure. And I know of no way to safely test "which way is this one wired?", when it comes to a sensor. It is, of course, easy enough to test the wiring in a socket meant to have a sensor plugged into it.

Sigh. Oh. And the labeling on some PCSensor USB 1-Wire adapters could be mis-read as saying that V_cc will be connected to the tip of anything plugged into them.on the tip is what is inside the adapter. As far as I know, all of the PCSensor 1-Wire adapters are what I am going to propose calling "Ground Tip" devices.

Does your bad day seem less bad now?

My "answer"

With all of my sensors and modules, I have labeled each sensor, each module, either "V_cc Tip" or "Ground Tip", depending on which way that item was wired. There are, at 9/11, suggestions on the PCSensors website, that they will be changing the wiring in the TEMPerLAN, so that new TEMPerLANs will come in the "Ground Tip" form. I hope PCSensors will adopt my idea of labeling everything "Ground Tip" or "V_cc Tip". If they don't, there will be a lot of confusion out there! And I would advise everyone to avoid any use of "standard" for wither scheme. Mr Murphy is watching. Just as soon as we start calling one or the other "standard", a decision will be taken to move forward with the other connection scheme as "standard". Using "V_cc Tip" or "Ground Tip", as appropriate, on every device will avoid the dangers of "standard".

We can at least be grateful for the fact that the 1-Wire data line remained on the central section of the 3.5mm plug! Because of that, the two alternatives are easy to distinguish, when you are dealing with a module a sensor needs to be plugged into.

It isn't so easy to tell which wiring applies to a given sensor.

The other good thing is this...

Once you have all of your sensors and modules labeled either "Ground Tip" or "V_cc Tip", the you can always plug two or more things together, as long as they are of the same type. And if you have several, say, "Ground Tip" devices, they can all be plugged together, and you can even add some "V_cc Tip" type components to that MicroLan with a simple adapter.

And all the adapters you will need are one type. And splitters and extender cables will all work in either sort of network.

So it could have been worse. But I bet PCSensors would still have rathered the whole mess didn't arise!

They posted a very nice apology on their website.

So go back to my main page about their products. Buy something! There are some great bargains, at the moment. Although I do moan about the state of software and documentation at 9/11, I do think the product line is good, and hope you will support it... so that PCSensors and others see some point in spending the money to develop software for the good hardware!

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