Using DT24 voltimeter

I’m quite new on using OpenMQTTGateway. My hardware is: ESP32. Question is: how should I read data from DT24 voltmeter. Acording documentation: i’ts supported but i require "connect to retrieve some parameters but I don’t know how should I “connect”. I know BLE address but I can’t see it on MQTT topic list. Please help.


You need to verify first that nothing else is connected to the DT24 (like your smartphone), after OMG will retrieve data to it every 550s, you need an MQTT client like MQTT explorer to check the history of the messages.

I’ve turned off BT on phone which I was using E-test app but on OMG I can see only topic with MAC, name and RSSI. No data from voltmeter! Any ideas?

Could you share the environment or binary that you are using for this?

I’m using: OpenMQTTGateway_ESP32_ATOM_BLE_IR v0.9.9. Upgraded from 0.9.8 via OTA from original binary repository (


I just updated my test ESP32 to that firmware version ( pro tip - GPIO 39 is always low on my ESP32 so I got stuck in a setup Wifi / Erase credentials loop and needed to redefine TRIGGER_GPIO ) and was able to connect to my DT24.

N: Send on /BTtoMQTT/200507161361 msg {"id":"20:05:07:16:13:61","mac_type":0,"name":"DT24-BLE","manufacturerdata":"733688a0200507151361","rssi":-84} N: BLE Connect begin N: Send on /BTtoMQTT/200507161361 msg {"model":"DT24","id":"20:05:07:16:13:61","volt":16,"current":0,"power":0,"energy":0,"price":2.01,"tempc":20,"tempf":68} N: BLE Connect end

Just a couple of comments to help you with this

1 - I find that the bluetooth range is limited and needs to be within a few meters of the DT24, if my ESP32 is in a different room it does not connect.

2 - I had just booted my DT24 and I was not running the App on my phone

3 - The discovery message and the voltage reading share the same topic, and by default connect runs every 10 scans aka 10 minutes

Range is not an issue (50cm between gateway and voltmeter). I can only see:

Topic: home/OpenMQTTGateway_ESP32_ATOM_BLE_IR/BTtoMQTT/35C97E8E8262
Value: {“id”:“35:C9:7E:8E:82:62”,“mac_type”:0,“name”:“UC96_BLE”,“rssi”:-67}
History for these topic (in MQTT Expolere) shows only these kind of messages.

I’ve bought voltmeter one these auction: 15 w 1 USB 3.1 Tester miernik prądu stałego woltomierz cyfrowy Voltimetro woltomierz Power Bank Wattmeter napięcie lekarz detektor|Voltage Meters| - AliExpress

I was using “E-test” android app (found somewhere) to read value from device. Is it possible that it’s NOT DT-24?

It’s not identifying as a DT24, hence the logic in OpenMQTTGateway is not able to retrieve the values. If you have the time and ability it may be using a similar message structure, service and characteristics so you might be able to get it to work. I know that when I did the original work with the DT24 I got very lucky and someone had already reverse engineered the bluetooth connection, so all I needed to do was transpose javascript into C.

I’ve ordered (and got) another DT24 voltmeter (1000V/0~1000A DT24P Digital Display DC Power Supply Voltmeter Ammeter Battery Capacity Tester Battery Fuel Gauge Meter|Voltage Meters| - AliExpress) According documentation (My Files) it’s DT24P. It broadcasts as E-test BLE. It uses the same android app but protocol must be different. I’ve recompiled current version of OMG with patches which forces to treat these devices (UB96_BLE and E-test BLE) as DT24 but it’s not working:

N: Device detected: 77:33:AC:73:03:8B
T: getDeviceByMac 77:33:AC:73:03:8B
T: Connectable device found: E-test BLE
T: getDeviceByMac 77:33:AC:73:03:8B
T: add 77:33:AC:73:03:8B
T: Device mac 77:33:AC:73:03:8B
T: Device UNKNOWN_MODEL 77:33:AC:73:03:8B
: Get services data number: N: BLE Connect begin
T: Model to connect found: 77:33:AC:73:03:8B
T: Converted service data (20) to 0000000000000000000000000000000000000000
T: Service data: 0000000000000000000000000000000000000000
T: Service data UUID: 0xfe9f
T: No device found 
T: Removing servicedatauuid
lld_pdu_get_tx_flush_nb HCI packet count mismatch (1, 2)
E NimBLEClient: "Connection failed; status=574 "
E: Connect to: 77:33:ac:73:03:8b failed

Any ideas how to start deal with it?

I have currently the same issue with another device of this type. I’m investigating and let you know.

Any news with new devices?