• FEMU 1.0.4.ty.01005 - RF needs changes

    femtoduino • 11/11/2020 at 10:03 • 0 comments

    Ok, so after working with Mike M. Volokhov (@mishkathebear on Twitter), it seems design 1.0.4.ty.01005 is a no go for Wi-Fi. If I understood correctly, it resonates at too high a frequency (sorry, I'm still learning). Here's the Smith chart and SWR, MAG plots with the current chip antenna and footprint.

    ...I will have to make another FEMU revision without the cutout, and attempt to make a more suitable ground plane clearance, perhaps with a different chip antenna.

  • FEMU 1.0.4 - Antenna stuff using Nano VNA v2

    femtoduino • 11/11/2020 at 07:24 • 0 comments

    Thanks to Mike M. Volokhov (@mishkathebear on Twitter), I've started work on pi network matching for the FEMU 1.0.4.ty.01005 design.

    Here is the initial Smith chart, SWR, and MAG

    ...I'll attempt to use different capacitor and inductor values. Suggestions welcome, as I am rather new to RF stuff.

  • FEMU 1.0.4.ty.01005 (revision 1 of 2)

    femtoduino • 08/13/2020 at 03:18 • 0 comments

    Hello everyone! Thanks to the overwhelming community support, this PCB revision is now being fabricated at PCBWay as of the time of this writing!

    The RF antenna trace and wave guide has been revised to work with an SMD monopole chip antenna. The RF Trace impedance was too high in 1.0.3, so for 1.0.4, it has been redesigned to be 0.5mm wide, and have an impedance of 35ohm+10j (as per the ESP32-D2WD datasheet notes). A wave guide calculator has been used.

    Once this order of FEMU 1.0.4.ty.01005 arrives, I'll need to test and match the RF design using a NanoVNA v2 (also thanks to community support!) while profiling the power usage with the JoulScope (thanks to JouleScope for lending me one for a bit!)

    Stay tuned!

  • FEMU 1.0.3 board respin, now testing ground plane and antennas

    femtoduino • 07/24/2020 at 20:22 • 0 comments

    Help me fund development of the FEMU open-source board (TOMU form factor!) https://Ko-Fi.com/femtoduino

    Next couple of batches need to be manufacturered with 1oz and 2oz copper pour, different ground plane configurations, and different chip antenna types!

    One set of prototypes will run around $570 (1oz copper pour), while the 2oz copper pour variant will be a bit more than $570, totaling a bit over $1140 for both.

    Current version 1.0.3 boards (0.8mm thick, 1oz copper) are mostly functional, but require ground plane adjustments (28cm max BT transmission at best). Currently experimenting with different antenna configurations.

  • FEMU 1.0.3 PCBs, FTDI EEPROM update, first MicroPython Example

    femtoduino • 05/21/2020 at 11:58 • 0 comments

    FEMU 1.0.3 has a revised RF layout and ground plane, along with more copper pour for the LDO footprint. I've also managed to break out both DAC pins. Currently testing the LDO at max throttle via the 2-layer prototype (larger, but same components).

    I've also figured out how to use ftdi_eeprom to adjust the behavior of the DTR and RST pins, and finally got the FT232XQ-R working nicely.

    If you're interested in making FEMU happens, buy me a coffee? ko-fi.com/femtoduino


  • Bluetooth UART working (with bodges)

    femtoduino • 10/16/2019 at 06:38 • 0 comments



    FEMU, with bodged RF inductor, appears to transmit just fine. There's some kind of issue going on with power supply, possibly related to grounding a few traces directly to the USB ground pin, and even more likely, due to the FTDI chip getting back powered at some point by the ESP32 chip... If I try any wireless stuff while plugged in to a computer, wireless stuff refuses to work. I modded a Bluetooth Arduino sketch I had (disabled all Serial comms), uploaded to the FEMU, and then powered the FEMU off a USB battery. Success! I was able to send a command and change the RGB color! Now...as to why two out of three RGB pins aren't PWMing... I'm not sure. There's more work to be done before I order another PCB revision. Stay tuned!

  • Working revision! (Mostly)

    femtoduino • 09/29/2019 at 18:58 • 0 comments

    At the very least, I've fixed the botched UART lines. I am able to flash MicroPython on to the FEMU. Unfortunately, I'm running into trouble trying to get REPL working with the latest esp-tool and MicroPython code base. I am going to troubleshoot it some more, but things seem to be manageable.