EEVblog Electronics Community Forum
Products => Computers => Embedded Computing => Topic started by: nfmax on April 20, 2021, 09:14:34 pm
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I have an application where one possible solution would be a remote I/O module, communicating over and powered by wired Ethernet. The inputs needed are two pulse input counters (for energy monitors), one or two push buttons, and an analog input for a temperature sensor - ideally something that will work with (and power) an existing 4-20mA current loop PT100 transmitter. Communication could be almost anything non-proprietary - MODBUS/TCP, MQTT, http or even telnet. I will not tolerate having to use a proprietary 'head end' software like Labview, it must work with one of the myriad protocols supported by Node-RED.
Should be reasonably small, and not outrageously expensive. Either a bare PWA or a boxed module would be OK.
Any suggestions?
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You could do a lot worse than a Raspberry Pi with an add-on PoE module... (For instance, you could put together an Arduino with Ethernet and PoE module. That would be worse.)
There are some PoE ethernet "Device Servers" available from the likes of Lantronix. Expect $150+ and no programability.
Wiznet has some nice hardware modules (no PoE, though, AFAICT), but I'm not sure whether they have any "read to go" software.
AFAICT, cheap wireless modules pretty much wiped out development of Ethernet widgets. Everything is pretty much frozen the way it was 15 years ago :-(
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And there is USB. I also searched for something with POE recently, because of unreliability of USB connectors, but to no avail. Maybe i will stick to USB, but with proprietary connectors, e.g. DSUB-9. Then i can use any of those cheap STM32 nucleo modules that i already know. I know USB isn't really for remote communication, but in my case it is about lab automation.
Regards, Dieter
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a TTGO board like this one : esp32, ethernet and poe on the same board. program with arduino.
https://www.aliexpress.com/item/1005002110968758.html (https://www.aliexpress.com/item/1005002110968758.html)
(https://ae01.alicdn.com/kf/H3b78be5e3bf74403aac2ecca5bf39a404.jpg)
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If you search ebay for "DSLRKIT Raspberry Pi 4 4B Active PoE Splitter USB TYPE C 5V Power Over Ethernet" there is something fairly cheap and universal. It splits a POE connection into ethernet and a 5 V supply with a USB C plug. They claim 2500 V isolation and 2.4 A output. This is meant for RPI but maybe useful for a STM32 development board as well. Need to order one to check it.
Regards, Dieter
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The first thing came to mind is Raspberry Pi, but from your need of pulse counters the Pi may need some help.
Then I remembered WIZNet W7500, basically a WIZNet W5500 + a Cortex-M0 MCU in one chip. For the PoE part you can use a TI PoE protocol chip + a ready-made 48V to 3.3V module, and there are MagJacks with PoE pins.
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I think I have a solution that will work. I combined a PoE splitter from Amazon https://www.amazon.co.uk/gp/product/B07TML96C9 (https://www.amazon.co.uk/gp/product/B07TML96C9) with a Devantech dS3484 Ethernet Relay Module from Robot Electronics: https://www.robot-electronics.co.uk/ds3484.html (https://www.robot-electronics.co.uk/ds3484.html). Despite the description, this module also has logic-level I/O and analogue inputs. It has inbuilt counter/timers, supports MODBUS/TCP, and can easily be configured using its own internal web interface. The only problem I found with it is its DHCP client seems to be a bit wonky, but I can live with that.
The splitter generates, and the dS3484 runs off, +12V, which luckily gives just enough headroom for the 4-20mA transmitter.
The best bit is, I already had one in stock, I bought a few years ago in an end-of-line sale at another distributor, just in case it might come in handy one day... :)