Teensy SDR

Teensy-SDR complete in enclosure

https://www.youtube.com/channel/UCz7YtteHS_qk7aumEbhIShg   (some interesting video’s how the TeensySDR is working)


A friend of my want to build the Teensy-SDR designed by Rich Heslip VE3MKC, so he asked me to test the software and made it ready for loading it in his Teensy 3.1. Because I like that challenge I bought a Teensy and set-up my Arduino IDE for the Teensy and start testing. Besides some missing libraries the software was compiling without further errors.


But the next question was to change the original 1.8″ TFT screen to a 3.2″ TFT screen. That was some more work but I also succeeded. But the only problem is that I did not have the needed Audio shield for the Teensy to do the audio work and also display the audio spectrum including a waterfall display.

I also bought a Sparkfun Teensy-Arduino adapter to make it possible using Arduino shields on the Teensy. This board is implemented and in use for testing the Teensy-SDR software. See the picture above.


A new Teensy-SDR design…
Things are going fast…  Frank, DD4WH has build his own Teensy-SDR based on the Teensy-SDR designed by Rich. He was willing to sent his software and I’m impressed how it looks.
Because this SDR uses a Real Time Clock, I installed the backup battery and the clock x-tal (which is part of the Sparkfun kit) and after compiling, the RTC was running, which you can see on the display. The next step is, after I received the Audio shield, to test the SDR and replace the 1.8″ 128×160 by a 3.2″  240×320 TFT screen ( I used a 3.2″ screen for the Raspberry Pi).

Important notice: When you are using the software of Frank beware to use the modified mixer.h file, added to the software suite from Frank. If you are using the wrong (not modified) mixer.h file you get a very bad unwanted sideband suppression at SSB. The mixer.h file is part of the Teensy Audio library.
You find this file at:   C:\Program Files (x86)\Arduino\hardware\teensy\avr\libraries\Audio

Teensy-SDR DD4WH

Teensy-SDR DD4WH

I have modified the software from Frank for using  a 3.2″ 320×240 pixel TFT display.  That was really a job because the positions of all the displayed functions should be changed. Especially the spectrum display was a challenge! Below you can see the results.  Frank has made 6 modifications on his software, which you can find (including the software) on the blog of Rich Heslip. See the link at the top of this page.

Download the Teensy-SDR software modified for the 3.2″ TFT screen (with permission of Frank DD4WH):
Latest version with better performance but not proper working sound recording from here or
Last but one version with good working sound recorder from here.
Needed Teensy-SDR libraries (si5351 and Time) download from here.
The schematic (wiring diagram) can be downloaded from here.

I’m using the Arduino IDE version 1.8.0.

Important notes:
Before starting the software you have to initialize the EEPROM by the following steps:
–  Remark (//) the EEPROMLOAD line in the Setup section of the sketch.
–  Set the right Si5351 x-tal frequency in the Setup section of the sketch.
–  Recompile the software and run the SDR.
–  Adjust the output frequency on CLK2 with the Set Cal factor.
–  Save your settings.
–  Remove the remark (//) from the EEPROMLOAD line.
–  Recompile.
–  Start the SDR.

Recompiling:  I found that the new Arduino compilers (version 1.8.x) are generating errors. Version 1.6.5 is compiling the SDR without errors (only some warnings).

Please let me know if you had found any bugs in the software.

Don’t forget to use the modified mixer.h file otherwise the SDR is not working OK, or make the modification by your self on two places in the mixer.h file:
// else if (gain < 0.0f) gain = 0.0f;
        else if (gain < -127.0f) gain = -127.0f;      (modification)

If you want to run the Teensy-SDR not only on USB power, you have to remove a small track between the two pads (left from the Vin pin) on the backsite of the Teensy board. See picture below.

It’s also a good idea to add an elco on the two big pads and add a diode on the two small pads so you can use the Teensy-SDR on USB- or 12V external power as well.


One of the new features was the addition of a notch filter. I have to say that the notch filter is working perfect. You can change the position of the notch in steps of 10 Hz left or right to the Rx center frequency.

Teensy-SDR 240x320 TFT

Teensy-SDR on a 240×320 TFT  (Notch is switched on)


Exploded view of the Teensy-SDR

Exploded view of the Teensy-SDR


This week (may 2016) I have build the Teensy-SDR in an enclosure made from PCB material. Front is made from laminated photo paper. I’m satisfied by the result….
My friend Joris decided to design a more professional PCB for the SDR front-end. Here you can download the schematic. In the Inside View picture below you can see on the right the (green) SDR front-end PCB.  For more info about that PCB and availability please contact Joris at:  kthkit[at]xs4all[dot]nl

Inside view

Inside view