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emonTx screw terminal block

(Dave Howorth) #1

Are the pinouts of the screw terminal block on the emonTx documented anywhere?

I’ve looked on https://wiki.openenergymonitor.org/index.php/EmonTx_V3.4 and on https://wiki.openenergymonitor.org/index.php/EmonTx_V3 but they both seem to have incomplete lists of the pin assignments:

Screw terminal pin Connection
1 5V (if powered via 5V USB)
2 3.3V
3 GND
4 IRQ 0 / Dig2
Screw terminal pin DS18B20 Connection
3 - GND GND (Black)
5 - Dig19 Power (Red)
6 - Dig5 Data (White)

Firstly, am I correct in assuming that these two lists document subsets of the same overall pin assignment list?

Then, am I right that pin 5 is 3.3 V? And that pin 1 has 5 V available iff there is a USB power supply? And that I could connect a DS18B20 daisy-chain to pins 1, 3 and 6 to use 5 V as recommended by Maxim on https://www.maximintegrated.com/en/app-notes/index.mvp/id/148 ? Or would that cause problems for the input?

Edit: the post from albundy in the discussion at
https://www.raspberrypi.org/forums/viewtopic.php?t=36163 may be relevant.

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DS18B20 reliability considerations
(Robert Wall) #2

Look on the underside of the PCB.

The drawings are either in the Wiki where you looked (I think?) or can be downloaded via the link there.

The 5 V rail is common to the screw terminals, the USB & FTDI connectors and the battery. The 3.3 V rail can derive from that, or from the a.c. adapter if link JP2 is present. There is no mechanism to derive 5 V from the a.c. adapter.

Pin 5 is a switched output from the processor. It will always be less than the 3.3 V rail.

There’s comment about the temperature sensors here: DS18B20 reliability considerations

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(Dave Howorth) #3

Ah thanks. It never occurs to me to refer to board layouts etc for pinout documentation. I suppose I’m so used to text documents.

I see the data line is pulled up to 3.3 V in all cases, so will be fine if the devices are powered from 5 V.

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