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Simple, Compact Wireless Measurement

No more getting up to probe and poke at a circuit deployed far away

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I work with wireless devices, and field testing is annoying because I have to get up every few minutes to measure a voltage if something goes wrong, or to check the voltage of a battery.

I designed a compact wireless device to do the basic measurements that I would be doing with a multimeter. The goal is to enable simple monitoring of other devices that I am prototyping. To operate it is simple: just plug it in and it will start streaming data immediately

I was starting to do this with a custom board design and wireless IC but I realized that I didn't need the complexity. I can do it with a few cheap, off-the-shelf modules, and other beginners can do it too.

There are other devices that do wireless measurements, but they are often features you only find in high-end measurement devices. With this device I hope everyone would have access to wireless measurement features.

Assemble it with completely off the shelf parts

Most aspiring hobbyists don't have a full SMT workstation. I didn't when I started out. I only had a crappy soldering iron. However you can also substitute modules here for off the shelf parts so that you can throw together a kit on a breadboard.

The caveat is that the overall build will be bigger. I have included the parts that can substitute each module below.

Requirements

1. Soldering iron (optional)

2. A phone or gatttool to see the data.

Use

Connect wires from the voltage or current measurement outputs. When the device is powered, the MCU will automatically start measuring voltages and pushing the converted values to the Bluetooth chip. The converted values are in the format "[voltage_1],[voltage_2],[current_1],[current_2]"

Assembly

Manufacture the board and solder the components on. If you prefer, you can also breadboard it.


Wireless

The JDY-08/HM-11 forms the wireless core of this project. It is an extremely cheap (<$2) Bluetooth BLE module that already has a complete set of AT-like commands preprogrammed. The key usefulness of this module is that it already has a transparent mode included as part of the application, which allows us to send arbitary sets of data to and from the IC.

MCU
To make it easily programmable, is paired with ATMega-328P, the 'Arduino' chip. This also means that you don't need a special board to use it. Simply use it as a shield for an Arduino Uno, wire it to a Teensy, or build your own board as I have done here.

Alternatively, use SiLab's Laser Bee MCU that is specifically designed to collect analog data and work at 3.3V.

Power
To make it usable and safe, it can take either an AA rechargeable or standard alkaline non-rechargeable battery. I think this provides better flexibility in power options - you can get batteries at a gas station, but it is unlikely you can do the same with a LiPo. I use a single battery here to minimize bulk, with a step-up voltage boost regulator to get it to 3.3V for the MCU and Wireless device.

Additional advanced functionality includes:

1. uA current measurement

2. Sleep mode

3. Logging

4. Graphing App

5. Record data in App (in development)

6. Pin toggling (in development)


Obtaining Data

To retrieve data very simple. simply use nRF connect app to scan for "JDY-" device. Once connected, first service will output the data from the wireless measurement.

If you really want the data collection to be remote, you can also use a Raspberry Pi 4's Bluetooth to scan and connect to the device. That way you can SSH in to grab the data.

You can also use the dedicated App to scan for and connect to devices, which will then display and graph the information from each of the terminals.


Limitations

1. This device is mainly used for measuring low-power wireless devices (3.3V). It can measure high currents and voltages, but would need modifications to the existing circuitry to do so. For high voltages, you'll need to create a voltage divider circuit in front of the input.

2. It doesn't have a noise rejection circuit

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  • JDY-08 Breakout & Voltage Measurements

    Lim Han Yang11 hours ago 0 comments

    So it turns out that you can even find the JDY-08 breakout from Aliexpress, which means that every part of this project is now easily breadboard-able! This means that even if you don't know how to solder, you can also build a measurement circuit yourself.


    Since this is meant for low voltage experimentation, it can only measure up to 3.3V. Using Arduino's native ADC which gives us 1024 counts (8-bits), if we increase the voltage range we can measure, the precision falls.


    Maybe one way is to create a switch so that you can turn on high voltage measurement whenever you want to, although I think that might already be a feature creep.

  • Alternative ICs

    Lim Han Yang2 days ago 0 comments

    The ATMEGA328P is not the best IC to do ADC measurements with, plus it is very out of stock.


    I'm thinking for the final design using a Laser Bee from Silicon Labs might do the trick. It is designed specially for measuring analog signals and it is quite a low cost part. It also has USART to pass messages to the BLE module, and it wouldn't need the finagling that the ATMEGA needs to run at 3.3V.

  • Current measurement for the JDY-08

    Lim Han Yang3 days ago 0 comments

    1. My breakout board for the JDY-08 draws about 9.5mA of power @ 3.3V, and this is approximately true even when it is transmitting.

    2. I have a pretty bright LED on the board so that can account for roughly 50% of the power draw.


    If I use the worst-case estimate: assuming a smallish 600mAh battery (1.2V) with a 60% efficiency, with another 5mA of power draw from the ATMEGA, that is 15mA from the circuit at 3.3V = 50mW vs 432mWh, this means that a fully charged battery can last about 8 hours of continuous power draw and measurement.


    Using an Alkaline battery with 2000mAh would give us approximately a day of measurement. I think this is a pretty good even without any power optimization.

  • Chip Shortage woes

    Lim Han Yang4 days ago 0 comments

    It is incredible how far this chip shortage has spread. I can't find ATMEGA328P TQFP packages at any of the people I like to buy from.

    I guess now I'll have to use the DIP version, although that's not too bad, since that means that the whole circuit can be prototyped on a breadoard.

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