FT-75B External Arduino VFO

[VK3ZYZ]

I thought I had posted the mod done on VK3BPH's FM-75B Arduino VFO but I cannot find it.
I'll have to dig the info up and do a post on it.
Today I started the mods for another FT-75B, this one from VK3GSR. The first one I did included mods to the radio, removing the 5 pin and 7 pin sockets used for the external VFO then adding a 5 pin DIN socket for the new VFO and installing a resistor ladder on the band switch for the Aduino to read. But this time, I want to eave the radio as standard so plugs are needed. There are hard to find so I made them.
The 7 pin "Valve" socket plug was put together from some pins out of mini XLR plugs, and I found a 7 pin valve pin straightener in my junk so that became the plug base. This picture shows a 9 pin straightener too. (They actually are 8 and 10 pins just to make fitting on the valve pins easier.)

The holes were drilled out to 1.5mm to suit the step on the pins.

For the 5 pin plug, some 2.4mm bronzing rods were pressed into service.

5 lengths were cut and the ends rounded a bit. Then wires soldered on and reinforces with dual wall heat shrink.
Heat proof tape was put over the 5 pin socket, the pins pushed through into place , a length of PVC pipe places over tit then hot melt glue pumped in. This is pretty rough but works ok. For the 7 pin plug, the resistor ladder was soldered into the pins, wires, and hat shrink tube added to make the band plug.

And they seem to fit!

I'll post more info later.

 

[VK3ZYZ]

Here are a couple of pictures of #1 mod.

EDIT: I have added a clarifier pot and the Crystal/EXT sense line. It is a bit different to the other board so a couple of ports are swapped over.
Here is the code...
After calibrating the Si5351 board (cal_factor) in the set, the FT75B is run on CW on each band and the error noted. This error (offset_cal) is added to the frequency to increase the accuracy of the signal. I got it to 10Hz and I'm happy with that.

// these will be different for each setup.....
int32_t cal_factor = 9200;                 // from "Examples/Etherkit Si5351/etherkit_calibration" sketch.
unsigned long offset_cal = 1165;           // calibrate FT-75B 5.1724Mhz internal offset crystal.

 

[VK3ZYZ]

I have a working setup now....




When the radio is using the internal crystals...


Then, switching to "EXT"....

The lower RH number is the clarifier. +/- 1Khz.
There is a bit of code cleaning up to do yet as on the high bands, the frequ changes often toggle between 000 and 999 in the least 3 digits for some reason. And the VFO does not always see the change from crystals to EXT until the encoder is moved, but that should be a easy fix (later as I have closed the box for now).

EDIT: I have just included the clarifier to the VFO on receive in the code.
EDIT2: Increased the drive and fixed the crystals/EXT display switching.
EDIT3: Included a calibration for FT-75B 5.1724Mhz internal offset crystal.

 

[VK3ZYZ]

Here are a few more pictures...
I added a steel plate (back of an old DVD machine case) that just sits under the cover. This allows me to use a magnet to fold the VFO on top of the set....



In position...

And the magnet I found is from a car antenna base.

The PCB wiring...






The receiver goes ok, but I suspect there is a fault with the transmitter. It does not transmit in crystals either.
To be continued!

 

[VK3ZYZ]

It works
I just had a contact with Jim, VK2QA, on 7.11Mhz (or there abouts) and found the HEATER lamp does not work.
The new code posted above looks ok. I still cannot get a good picture of the LCD!