Is there a gadget I can attach to a wall plug that will send/shows voltage?

[Merlysys]

Ideally it should send voltage at wall via Bluetooth to an Android app so it can be viewed as a graph.

I have a DMM but while it shows current voltage I have no way to monitor it for a day.

[brucehoult]

Ideally it should send voltage at wall via Bluetooth to an Android app so it can be viewed as a graph.

I have a DMM but while it shows current voltage I have no way to monitor it for a day.

I use TP-Link "Tapo" P110, 4-pack for $28 on Amazon.

Code: [Select]

bruce@i9:~/p110$ cat emeter
#!/bin/env python3
import asyncio, os
from kasa import Discover  # pip install python-kasa

async def main():
  try:
    dev = await Discover.discover_single("192.168.1.41",
        username="bruce@myemail.com", password="mytapopassword")
    print(await dev.protocol.query({"get_emeter_data": None}))
  finally:
    await dev.disconnect()

asyncio.run(main())
bruce@i9:~/p110$ ./emeter
{'get_emeter_data': {'current_ma': 9764, 'voltage_mv': 242220, 'power_mw': 2301853, 'energy_wh': 8530}}
bruce@i9:~/p110$     

Call it as often as you want. The stand-alone script takes 0.25 seconds to run on my machine.

Code: [Select]

bruce@i9:~/p110$ while true ;do echo -n `date`;./emeter;sleep 5;done
Mon Sep 7 23:20:44 NZST 2026{'get_emeter_data': {'current_ma': 9610, 'voltage_mv': 241679, 'power_mw': 2278483, 'energy_wh': 8749}}
Mon Sep 7 23:20:50 NZST 2026{'get_emeter_data': {'current_ma': 9618, 'voltage_mv': 241707, 'power_mw': 2268430, 'energy_wh': 8752}}
Mon Sep 7 23:20:55 NZST 2026{'get_emeter_data': {'current_ma': 9655, 'voltage_mv': 241833, 'power_mw': 2264753, 'energy_wh': 8755}}
Mon Sep 7 23:21:00 NZST 2026{'get_emeter_data': {'current_ma': 5584, 'voltage_mv': 245126, 'power_mw': 1114037, 'energy_wh': 8758}}
Mon Sep 7 23:21:06 NZST 2026{'get_emeter_data': {'current_ma': 5043, 'voltage_mv': 245042, 'power_mw': 1118496, 'energy_wh': 8759}}
Mon Sep 7 23:21:11 NZST 2026{'get_emeter_data': {'current_ma': 5032, 'voltage_mv': 245053, 'power_mw': 1121582, 'energy_wh': 8761}}
Mon Sep 7 23:21:16 NZST 2026{'get_emeter_data': {'current_ma': 5079, 'voltage_mv': 245043, 'power_mw': 1130491, 'energy_wh': 8763}}
Mon Sep 7 23:21:22 NZST 2026{'get_emeter_data': {'current_ma': 3663, 'voltage_mv': 245111, 'power_mw': 707353, 'energy_wh': 8764}}
Mon Sep 7 23:21:27 NZST 2026{'get_emeter_data': {'current_ma': 3644, 'voltage_mv': 246045, 'power_mw': 706119, 'energy_wh': 8765}}
Mon Sep 7 23:21:32 NZST 2026{'get_emeter_data': {'current_ma': 4125, 'voltage_mv': 245609, 'power_mw': 859876, 'energy_wh': 8766}}
Mon Sep 7 23:21:37 NZST 2026{'get_emeter_data': {'current_ma': 4165, 'voltage_mv': 245609, 'power_mw': 861920, 'energy_wh': 8768}}
Mon Sep 7 23:21:43 NZST 2026{'get_emeter_data': {'current_ma': 4576, 'voltage_mv': 245315, 'power_mw': 1015772, 'energy_wh': 8769}}
Mon Sep 7 23:21:48 NZST 2026{'get_emeter_data': {'current_ma': 5048, 'voltage_mv': 245049, 'power_mw': 1120068, 'energy_wh': 8771}}
Mon Sep 7 23:21:53 NZST 2026{'get_emeter_data': {'current_ma': 5618, 'voltage_mv': 244713, 'power_mw': 1269805, 'energy_wh': 8773}}
Mon Sep 7 23:21:59 NZST 2026{'get_emeter_data': {'current_ma': 5653, 'voltage_mv': 244561, 'power_mw': 1293534, 'energy_wh': 8774}}
Mon Sep 7 23:22:04 NZST 2026{'get_emeter_data': {'current_ma': 6174, 'voltage_mv': 244389, 'power_mw': 1414544, 'energy_wh': 8777}}
Mon Sep 7 23:22:09 NZST 2026{'get_emeter_data': {'current_ma': 6800, 'voltage_mv': 243928, 'power_mw': 1571879, 'energy_wh': 8779}}
Mon Sep 7 23:22:15 NZST 2026{'get_emeter_data': {'current_ma': 6940, 'voltage_mv': 243524, 'power_mw': 1706748, 'energy_wh': 8781}}
Mon Sep 7 23:22:20 NZST 2026{'get_emeter_data': {'current_ma': 7291, 'voltage_mv': 243583, 'power_mw': 1698077, 'energy_wh': 8784}}
Mon Sep 7 23:22:25 NZST 2026{'get_emeter_data': {'current_ma': 7842, 'voltage_mv': 243291, 'power_mw': 1835642, 'energy_wh': 8786}}
Mon Sep 7 23:22:31 NZST 2026{'get_emeter_data': {'current_ma': 9614, 'voltage_mv': 242156, 'power_mw': 2273893, 'energy_wh': 8789}}
Mon Sep 7 23:22:36 NZST 2026{'get_emeter_data': {'current_ma': 9631, 'voltage_mv': 242263, 'power_mw': 2273668, 'energy_wh': 8793}}
Mon Sep 7 23:22:41 NZST 2026{'get_emeter_data': {'current_ma': 9618, 'voltage_mv': 242257, 'power_mw': 2271018, 'energy_wh': 8796}}
^C
bruce@i9:~/p110$


[Aldo22]

Ideally it should send voltage at wall via Bluetooth to an Android app so it can be viewed as a graph.

I have a DMM but while it shows current voltage I have no way to monitor it for a day.

Do you really want to monitor the mains voltage?

Or the power consumption of your devices?

[brucehoult]

Ideally it should send voltage at wall via Bluetooth to an Android app so it can be viewed as a graph.

I have a DMM but while it shows current voltage I have no way to monitor it for a day.

Do you really want to monitor the mains voltage?

Maybe they have their reasons.

Or the power consumption of your devices?

What I showed does that too, showing the cumulative Wh for that device today.

And for that you can see in the app the hourly totals for the last seven days, the daily totals for the last three months, and the monthly totals for the last couple of years.

[voltsandjolts]

Maybe they have their reasons.

I know of someone who lived close by an industrial estate. He found that at night, with little industrial activity and low loading, the mains voltage increased to 260V.

[studiot]

Maybe they have their reasons.

I know of someone who lived close by an industrial estate. He found that at night, with little industrial activity and low loading, the mains voltage increased to 260V.

I had a similar experience,with costly results.

[brucehoult]

Maybe they have their reasons.

I know of someone who lived close by an industrial estate. He found that at night, with little industrial activity and low loading, the mains voltage increased to 260V.

I had a similar experience,with costly results.

260 shouldn't be a problem.  253V is within spec.

A couple of years ago there was a fault in the transformer at the road, 300m away, and one of my phases was 140V and the other was 340V.

A couple of things on 340V let out magic smoke, and a couple of things with motors didn't work on 140V (my coffee machine) and the oven took three times longer than usual to get to pizza-making temperature.

But surprisingly 90% of my things just didn't care at all.

[Aldo22]

Depending on what you mean by “attach to a wall plug,” maybe a CM2100B could be a solution?
It can collect data and transmit it to a smartphone via Bluetooth.
Here are some pictures:
https://www.eevblog.com/forum/testgear/owon-cm2100b-is-uni-t-ut210e-inspired/msg6179965/#msg6179965

[brucehoult]

Depending on what you mean by “attach to a wall plug,” maybe a CM2100B could be a solution?

$99. Plus you're going to need an AC line splitter.

[Aldo22]

Depending on what you mean by “attach to a wall plug,” maybe a CM2100B could be a solution?

$99. Plus you're going to need an AC line splitter.

I don't know how much it costs elsewhere, but here it's about 56 €, including tax.

You don't need a line splitter for measuring voltage.

I'm not exactly sure what Merlysys wants.
Maybe more of an energy meter, maybe more of a DMM.
Maybe he'll tell us.

[studiot]

https://www.amazon.co.uk/OWON-Monitoring-Measurement-Integration-High-Power/dp/B0DCJTNNNG/ref=asc_df_B0DCJTNNNG?mcid=eb646620e487319eb7f0bdf90d2b7230&tag=googshopuk-21&linkCode=df0&hvadid=710973125435&hvpos=&hvnetw=g&hvrand=3941044394568601733&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9045348&hvtargid=pla-2369654455424&hvocijid=3941044394568601733-B0DCJTNNNG-&hvexpln=0&gad_source=1&th=1

[brucehoult]

https://www.amazon.co.uk/OWON-Monitoring-Measurement-Integration-High-Power/dp/B0DCJTNNNG/ref=asc_df_B0DCJTNNNG?mcid=eb646620e487319eb7f0bdf90d2b7230&tag=googshopuk-21&linkCode=df0&hvadid=710973125435&hvpos=&hvnetw=g&hvrand=3941044394568601733&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9045348&hvtargid=pla-2369654455424&hvocijid=3941044394568601733-B0DCJTNNNG-&hvexpln=0&gad_source=1&th=1

I see USD$183 for that.

My solution is under $10 for one .. and actually I just saw it's got up to $36 for a 4-pack (I said $28 before). But that's still only $9 each.

https://www.amazon.com/Tapo-Compatible-SmartThings-P110M-4-Pack/dp/B0DKG52WQ4

If you really only want one (why??? They're soo useful .. I have ten right now) it's $9.99

https://www.amazon.com/TP-Link-Tapo-Compatible-Certified-P125M/dp/B0BNWGZ545

[I don't know why people can't trim their freaking URLs when posting them!]

[ledtester]

If you want one that doesn't use a cloud service, check out the Shelly power meters, e.g.:

https://www.amazon.com/Shelly-Bluetooth-Automation-Compatible-Schedules/dp/B0CQCNKVD4

Accessible via Bluetooth and Wifi.

[TUMEMBER]

https://www.amazon.co.uk/OWON-Monitoring-Measurement-Integration-High-Power/dp/B0DCJTNNNG/ref=asc_df_B0DCJTNNNG?mcid=eb646620e487319eb7f0bdf90d2b7230&tag=googshopuk-21&linkCode=df0&hvadid=710973125435&hvpos=&hvnetw=g&hvrand=3941044394568601733&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9045348&hvtargid=pla-2369654455424&hvocijid=3941044394568601733-B0DCJTNNNG-&hvexpln=0&gad_source=1&th=1

I see USD$183 for that.

My solution is under $10 for one .. and actually I just saw it's got up to $36 for a 4-pack (I said $28 before). But that's still only $9 each.

https://www.amazon.com/Tapo-Compatible-SmartThings-P110M-4-Pack/dp/B0DKG52WQ4

If you really only want one (why??? They're soo useful .. I have ten right now) it's $9.99

https://www.amazon.com/TP-Link-Tapo-Compatible-Certified-P125M/dp/B0BNWGZ545

[I don't know why people can't trim their freaking URLs when posting them!]

Maybe start a thread explaining how to do it for future users. At least some of them might start using the method, and you’d stop getting annoyed. After all, this is the "Beginners" section. If a moderator were to "pin" the thread at the top of the section, it would stay visible for more than just an hour; otherwise, it’ll just disappear again into this "Augean stable."

[brucehoult]

It varies from site to site. Removing any '?' and whatever follows it is usually a good start. And check if that still works. For Aliexpress that's enough. In the case of Amazon the '/ref=' is also unnecessary.