Radio Board v2

After a too long break we finally got back to debugging the problems in the radio boards.

RF measurements

RF measurements

There was’t actually anything seriously wrong, mainly smaller issues that together made things look worse than they were. Version 1 did have some hardware design bugs but they were quite quickly spotted.

The first prototypes don’t work together with the ITead boards because there seems to be 50kHz offset in the radio frequency. That might be because the first prototypes are single sided while the reference design assumes double sided. We are not RF engineers so it might be anything else as well ๐Ÿ˜‰

It also turned out that soldering 0.5mm pitch VQFN chips without proper tools or experience can easily leave some pads unconnected. Combining that with initial software and interoperability problems with the old boards, things were not looking good. After figuring out these deficiencies we started to make good progress again.

Radio board with a battery

Radio board with a battery

Now we have couple of reworked v1 boards with the TMP275 temperature sensor and they are working reliably. The software is measuring the battery voltage using ADC and getting the temperature over I2C from the TMP275 and sending both over the air.

We have done also some tests with the low power modes. The whole board consumes 7uA in a sleep mode:

Radio board power measurement

Radio board power measurement

The low consumption is in LPM3 with ACLK running so that the chip can wake up using a timer interrupt. It should be possible to get down to 1uA in LPM4 but it’s still a bit unclear to me if that needs an external signal to wake up. Even with 7uA we are quite confident that long operating times with small batteries are achievable ๐Ÿ™‚

Now that the boards are working, we fixed the design bugs and ordered v2 boards from ITead. Hardware-wise next step is testing different antennas to achieve good range with small antennas and software-wise we’ll combine the low power modes with temperature measuring.

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14 Responses to Radio Board v2

  1. ginpb says:

    Great project, what is the maximum range you get?
    Is range the reason you decided to go with an external antenna instead of a PCB one?

  2. Tuomas Kulve says:

    We haven’t made any proper range tests yet. Currently the range doesn’t seem too good (barely from corner to corner of my apartment) but I used an antenna that wasn’t tuned exactly to 433MHz. Also the initial prototypes were single-sided were the reference design is for two-sided and the first ITead prototypes are 1.6mm thick where the reference is for 0.8mm.

    We are planning to test several antennas with the new prototypes to get a better understanding how different types of antennas affect the range. We are also trying to figure out if it would be possible to test PCB antennas with the new prototypes.

    The new PCBs were just shipped from ITead so they should arrive after a couple of weeks. Then we need to learn a way to solder those VQFN chips more reliable.

  3. ginpb says:

    what data rate are you using?

    • Tuomas Kulve says:

      115200 bps. For temperature measuring something much slower with better error correction would be better.

      I’ve also used the radio as a wireless UART and for that the 115200 is needed.

  4. ginpb says:

    and what output power are you using?

    • Tuomas Kulve says:

      +0dBm. I tried also +10dBM but that didn’t improve situation significantly. We need to do more comprehensive tests with the new boards. I just today ordered all the components for the boards so now both the boards and the components are on their way.

  5. ginpb says:

    any news?

    • Tuomas Kulve says:

      We just got the boards. Hongkong post had a shipment delay and it took couple of weeks longer than usually to get the boards.

      We are aiming to get the first version 2 boards assembled within a week.

      I already got two 433MHz antennas that I tested with the current v1 boards and they seem to provide better range. We still need to do more precise testing with them.

  6. Janne Langi says:

    Moi Tuomas!

    This is interesting! I would need a bunch of wireless temp (and humidity) sensors for our new house. How would one receive the data from these to a linux box, for example?

    • Tuomas Kulve says:

      Well, if the linux box happens to be e.g. a Raspberry Pi, you can just hook up the UART TX/RX pins and you receive the data to RPi as they both use 3.3V UART.

      For a PC, you would need an UART to USB converter for the same.

      I started to work on a debug board that would allow one to hook the Radio Board easily to RPi and it would also include the UART to USB converted for easy PC access. But haven’t made much progress on that so far.

  7. Kafes says:

    Heya! It seems I’m a little late but this cute-little boards are awesome!
    How much does it cost per board and what is the maximum range?

  8. Tuomas Kulve says:

    If you build a few by yourself it’s about 15-20$ each.

    The range is a bit harder question. It’s supposed to be hundreds of metres with line of sight but I’ve only witnessed a few tens of meters. And inside a house we talking only about 5-15 meters, depending on the walls.

    But the antenna matters much when talking about range and I haven’t done any good comparison of those.