Replacing the Teensy 3.2 with 4.0 in the GQRP SCD Sudden Digital VFO

 Place holder for GQRP SCD Digital VFO Post

 

The chip shortage has struck down the Teensy 3.2 which was used in the GQRP Digital VFO here:

https://www.gqrp.com/suddenvfo.htm

 

Obviously that's a problem. 

However, there is light at the end of the tunnel, the Teensy 4.0 is pin compatible so could be a drop in replacement. 

 I downloaded the 'sketch' and tried to compile it, which failed with what looked like potentially simple to resolve errors and a *lot* of warnings about unused and uninitialised variables.

The information below shows the changes I made to the V0_13 sketch and get a successful compile.

 

Compiled for Teensy 4 using Arduino IDE:

Version: 2.1.0
Date: 2023-04-19T15:31:10.185Z
CLI Version: 0.32.2

Errors with unmodified sketch when compiled for Teensy 4

 "Sorry, i2c_t3 only works on Teensy LC and 3.x.  Use Wire for Teensy 4.0, 4.1, MicroMod."

To fix:

Change every instance of i2c_t3.h to wires.h

In: 

SCD_2021_V0__13.ino

Si5351.h

Si5351.cpp

To mop up some warnings, initialise the variables in display_functions.h :

void display_update_vfo(){

 

      // ------ variables used for vfo uodates etc.

      String freqt=String(u.vfo_A_value);    // Text frquency convertrd

      char F100m=0,F10m=0,Fmega=0,F100k=0,F10k=0,F1k=0,F100=0,F10=0,F1=0; //EachdDigit for VFO A

      char f100m=0,f10m=0,fmega=0,f100k=0,f10k=0,f1k=0,f100=0,f10=0,f1=0; //EachdDigit for VFO B

 

Comment out the variable declarations on lines 507, 807-810:

//      int freqMulti;

 

//      char F100m,F10m,Fmega,F100k,F10k,F1k,F100,F10,F1; //EachdDigit for VFO A

//      char f100m,f10m,fmega,f100k,f10k,f1k,f100,f10,f1; //EachdDigit for VFO B

//      int freqMulti;

//      int freqlength;

 

At this point and with a successful compile I decided to breadboard the circuit to see if things worked as they should.

Following the supplied schematic lead to this:

 

Success!

Still need to test the I/O lines to see if there's side tone, the encoders work etc. but it looks very promising.
 

Breadboarding the full circuit was rather flaky and unreliable so I put a request on the GQRP mailing list and got my hands on a V1 PCB 

Videos on YouTube (opens new tab) 

Sudden Digital VFO

Sudden Keyer Test