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15x ZHT-103 + Arduino Mega / Design validation
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alexromain 1 week ago
Hi guys, Thanks in advance for your patience, I discovered EasyEDA a few days ago .. (but spent quite some time on it since then and love it ! :) ) I need to create a board (actually, 5) that will interconnect an Arduino MEGA and 15x ZHT-103 sensors. The MEGA is already equipped with an ethernet shield. It’s a simple design, I got it working straight forward with 1 sensor and just 'adapted' by adding more sensors .. but before ordering and soldering the all thing, I would like some kind of confirmation =) I'm not certain that powering the thing the way it is (the MEGA powers the all thing, he's getting 9V as input through DCA.) is the key, nor if capa and resistances are still correct or should be adapted  .. Thanks a lot in advance to those who'll throw an eye on it :) Any comment welcome. [<span class="colour" style="color:blue">https://easyeda\.com/editor\#id=\|4d16cd6c5c9c481384d19dc363bf095d\|438fdd5409314760a6e2a77b61c9756a</span>](https://easyeda.com/editor#id=%7C4d16cd6c5c9c481384d19dc363bf095d%7C438fdd5409314760a6e2a77b61c9756a)<br> <br> ZHT-103 datasheet : [<span class="colour" style="color:blue">https://datasheet\.lcsc\.com/lcsc/2201121700\_ZHT\-ZHT103\_C2935356\.pdf</span>](https://datasheet.lcsc.com/lcsc/2201121700_ZHT-ZHT103_C2935356.pdf)
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alexromain 1 week ago
Hi Andy, First of all, thanks a lot for replying, this is really appreciated. The goal of this thing is to determine wether or not a lamp is ON or not. I did setup a complete domotics system based on sensors / arduinos / MQTT server / NORE-RED. This specific part of the setup works as followed : The phase cable of every lamp circuit in the house passes by a ZHT-103 sensor. This sensor is monitored by an arduino that reports his value to the MQTT server. NODE-RED monitors the MQTT info and reacts based on the value. I don't need a precise information, I just need to know whether the lamp is 'ON' or not. It works quite well with 1 sensor and the following setup : ![Capteur de courant ZHT103 par Mat99 - OpenClassrooms](https://user.oc-static.com/upload/2019/09/13/15683258858807_circuit-20190912-1951.png) What I need now is to multiply the quantity of sensors (up to 15) on a nice board that allows me to organise cabling properly. That's what I tried to do .. :) Now, lets answer point by point : 1\. SW1 should allow me to reset the arduino by connecting RST and GND when the button is pressed\. I tried to find a simple '2 poles' press button in the libraries but didn't find any\. Maybe I made a mistake on the cabling\. I thought that 1 and 4 would connect when the button is pressed\. Not correct ? 2\. Actually\, I only tried to reproduce the schematics that I joined here up with the 2x 10k resistances and 1x 100µF \(which is the setup that is actually working with 1 sensor\)\. I do not master that part of the thing \.\. :'\( 3\. I absolutely have no idea \.\. I just reproduced what I saw on the Internet concerning this setup and it worked well \(with 1 sensor\)\. 4\. The IN net is 'getting out' of the Arduino's \+5v and GND and passes by the resistances and capacitor as shown on the picture\. 5\. I hope I got clearer with this message and that it will allow you to confirm the setup or tell me what to correct to get it working :\) As mentioned, I don't need a precise info. What I need is 'there's current passing by' or 'there's no current passing by'. This info is needed to update the status of the lamps in my domotics installation. I hope these infos will help you helping me :) Thanks a lot in advance !!
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andyfierman 1 week ago
1. SW1 does nothing because the RST and GND connections are on separate poles of the switch. 2. It is not clear what the purpose of R1 and R2 is. They are identical NTC thermistors which are placed closely together on the PCB and so more or less are subject to the same temperature. Hence they will have about the same resistances. Hence the voltage at IN will pretty much appear to come from a Thevenin equivalent source of a constant 2.5V from a resistance of half the resistance of the thermistors at any given temperature. 3. The ZHT103 is a current transformer. It is not clear that the 100Ohms value of the internal burden (Load) resistor quoted in the ZHT103 datasheet is appropriate for your application. Without an appropriate burden resistor the CT will not function correctly and may destroy the Arduino inputs;  4. There is no connection of the IN net to the Arduino shown in the schematic. It is unclear that the IN connection can support the multiple connections as shown because the input impedance of the Arduino inputs and how you process the signals are not given in your post;. 5. You have however given insufficient information in the form of a Design Requirements Specification, a How-It-Works sort of document or any indication of your usage case so it is not possible to comment further about this configuration other than to refer you to some information below about what a current transformer is and how to use it: [https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/introduction](https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/introduction)<br> <br> [https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/interface-with-arduino](https://learn.openenergymonitor.org/electricity-monitoring/ct-sensors/interface-with-arduino)<br> <br> Note also that - although this aspect of their usage is poorly documented - current transformers can only be used reliably within their specified frequency ranges. The frequency range can be extended somewhat by reducing the value of the burden resistor shown in "2" or by using the circuit "1" in: [https://datasheet\.lcsc\.com/lcsc/2201121700\_ZHT\-ZHT103\_C2935356\.pdf](https://datasheet.lcsc.com/lcsc/2201121700_ZHT-ZHT103_C2935356.pdf)<br> <br> Without a given value for the CT winding inductance and the recommended burden resistance however the calculation of frequency response is somewhat speculative.
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