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The FT-7 AND AN ESP32 VFO  
 
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A digital display and VFO for the FT-7

The Yaesu FT-7 Transceiver is a product of the late 70's and early 80's, a 5 band HF Transceiver.

It uses an Analogue VFO and display.



It would be nice to 'update' the FT-7 a little by adding a digital VFO using a low cost Si5351 device and some sort of digital display.

We are not talking here about commonly available, simple external displays which just display the VFO signal (with band offsets). The idea here is for a fully integrated (internal) display to replace the analogue one, and also to digitise the VFO itself using the ubiquitous Si5351.


Possible ways to add the digital VFO/Display

Since repairing an FT-7 recently, thoughts turned to adding the Digital updates as above.

Searching the Web found a couple of projects by builders, but lacking in some details.

7-Segment LED display:

This is probably one of the easier mods to make in that well understood 7-segment displays can be used. Single or multiple digit displays are easy to obtain on eBay for example. To actually fit say, a 6 digit display, to give resolution of 100Hz, displays of around 7.6mm wide for each digit can easily fit into the approx. 50mm wide VFO display window of the FT-7.

An Arduino "NANO" or just the ATMEGA328P can easily drive these displays via a MAX7219 for example, which is the simplest way to multiplex the 6 digits.

In VK3, the MAX7219 is only easily obtainable (ie next day delivery) from the international vendors, Element14/Farnell but the devices are very pricey, in the order of AUD$16. Ebay is another possible source. I decided to buy an eBay 8 digit display and remove the MAX7219 from it, as the most economical solution for me at least. These displays use 2 x 4 digit devices which are too large for the FT-7 though.

I have since found that there is a Chines made "equivalent" for the MAX7219 for about $2. I have not tried one of these.

Here is a draft picture of a test bed 7-segment type display and VFO I will try initially. The PCB is 50x100mm but breaks into several sections, with the actual 6 digit LED display (bottom of pic) being mounted in the FT-7 dial window area.

APRIL 22nd, 2019:- The above PCB has now been tested with some software based on the work by VK3HN, for his portable SOTA rig. (Summit Prowler IV) I altered his sketch to change the display from his OLED type to my LED display using a LIB obtained on the web. ("DigitLedDisplay") and also implemented band selection using 5 inputs which are derived from the five band switch in the FT-7.

One problem found, was the 6 digit LED "3661AS-1" display I ordered from eBay, had a different pin-out to the actual Data Sheet! I had to hand wire the PCB section for the display. Not sure how to get around this problem, as I can only rely on the vendors description and information. It 'might be' that a "3661AS" has the correct pin-out, if one could find such a part on ebay.

A nice to have, blinking the digit of the currently selected one being tuned by the Encoder was also done. So far it looks likes it could be integrated into the FT-7 and work to replace the VFO at this point of development. An Si5351 is controlled by the Arduino NANO also and puts out +7dBm. I am yet to determine what actual level is required. This will be easy enough, as the FT-'s VFO output is a connector on the rear of the VFO housing. Just un-plug and measure the levels. Assuming 50ohms perhaps load?

You can see my very 1st youtube video here of the board above, working.

There are many other possible additions though. eg Memories for favourite fequencies. Clarifier etc.

A "better" approach:

An incredible FT-7 display, visually, might be obtained using the work of "Tj Lab", whose videos appear on uTube here. It visually emulates the analogue display of the FT-7 almost exactly, plus providing a multi digit display also.

He provides information on two versions of display, using OLED and TFT displays. The controller though is well beyond the humble NANO, a very fast Micro is required. In this case the ESP-32/ESP32s™ development board (eBay). Since I have a similar 1.8" TFT display already, I decided to try this approach. His Sketch is incomplete in that no band changing inputs are provided for example as the project was just to demonstrate the VFO in isolation. Initally I will duplicate his work, then see if I can modify it specifically for the FT-7.

This approach is overkill of course, and probably more expensive, compared to the 7-segment LED way, but sure has a lot of "wow" factor as you can see! Or "bling" as some may say. CLICK ON uTUBE VIDEO BELOW.

 

UPDATE, May 9th 2019. I have put together a test board to try this sketch out for the ESP32. (see PCB pictures below) I didn't use the same development board version as I couldn't find a source for it. The ESP32 board I did find is only about US$5.50, cheaper anyway. But not all Ports are bought out on this board. (it has 30 pins) I had to alter the port allocation for the Encoder only and do the appropriate change to the sketch #defines. I used D34, D35. The schematic provided by TJ_Lab has to be modified for the ESP32 I used.

I compiled tj's TEST code without errors and downloaded it to the ESP32 board. Initially I had problems with this, but found the "BOOT" button needs to be pressed to allow it to work. And work it does, very nicely. Especially nice is the variable speed of the dial, according to the speed of the encoder knob. Brilliant ! The 1.8" display I used is not the exact type specified, but one that does use the same controller chip. Display is about $4 from memory. Different pin-out also.

John, G3ZQC, is also working on this project with me. He is the C++ man, I do testing, and some minor code changes. Right now, it's working well as a 5 band (connected from the FT-7's 7 band switch) VFO running 5-5.5MHz and correct dial frequency display for each band, which suits the FT-7. Other rigs could no doubt be accommodated using these ideas. The Si5351 is working well also. Jim, G3ZQC, is another working with the ESP32 VFO.

The software also incorporates additions which cater for using a standard cheap mechanical encoder, or a high pulse count, quality optical encoder by changing a 'divide' ratio in the added "config.h" file. In fact, a number of compile time options are provided for.

 

12th April, 2019:- Mechanical considerations:

The display itself should fit into the existing display window of the FT-7. Since we are changing to a digital VFO also, then all of the existing VFO and slow motion dial mechanics are no longer required and can be removed. The VFO knob though is retained to fit onto the digital encoder which will be used to tune the radio now. The VFO itself is contained in a shielded box area which can be fairly easily removed and kept if one wants to revert back to the old VFO, at some later time. The project could also be built as an external VFO although it will be limited, in that, band selection of the VFO would have to be manual. Internal to the FT-7, we can pick off band selection from the rotary switch by freeing up the FIX position. For use on other HF rigs, the builder can interface to unused pins (ports) as required, with suitable software changes.

Some method of holding the new Encoder, Si5351 and Micro-controller will of course be needed. See below for possible PCB.

Components that I used:-

I bought all of the parts for this project from eBay. Rather than give details of the vendor I used, I will show the exact parts in picture form.

For the display, search for "ST7735 display" or similar. You will find a number of them but if you look for the type shown here, within that search, it should be OK.

The OLED type that TJ tried is very expensive so I didn't buy one of them.

I also found the same display that TJ used on eBay. It just arrived today so I have not tried it yet but can't see any problems. It is however a slightly smaller PCB at 58 x 35mm, than the one above which is 63 x 38mm, but the display area is the same at 1.8".

 

The ESP32 I used is a little different to that by TJ. It has less pins and cost was about US$5.50. In eBay, search for ESP32 and look for a similar board to this.

Click picture for larger size.

There is nothing on the bottom of the PCB except for the pins, so I won't show them.

To connect to the Schematic by TJ, just follow the pin connections in the ESP32 that I have. You will find though that this ESP32 is missing the two pins required for the Encoder. So, instead of using 16 & 17, use D34 & D35. In the "VFOsys_astep.ino" sketch provided by TJ, you will need to find these lines:-

#define PULSE_INPUT_PIN 16 //Rotaty Encoder A

#define PULSE_INPUT_PIN 17 //Rotaty Encoder B

and change them to

#define PULSE_INPUT_PIN 34 //Rotaty Encoder A

#define PULSE_INPUT_PIN 35 //Rotaty Encoder B

 

For the optical encoder I used a 360 pulse per turn type. Search eBay for "optical encoder". You will find a number of them similar to what I have. NOTE: TJ specifies a 40 pulse per rotation type of encoder. I actually divided down the pulses from my encoder using a ATtiny85 device (8 pin DIP) with a special sketch by G3ZQC. I won't detail that here for now. Amateurs skilled in programming no doubt could integrate the division into the ESP32 also. See the update above for 9th May 2019, as this facility is in a new Sketch.

The Si5351 board.

There are a number of Si5351 boards available. One common one is that sold by Adafruit Check their web page. No doubt similar ones are also available on eBay although I have not tried them. Most of these boards do not include any DC blocking capacitors on the output so you should add them. My application is for a VFO replacement in an FT-7 and only one source covering 5-5.5MHz is required. The Si5351 output is a square wave and I plan to fit a Low Pass Filer (LPF) on the output of mine to better suit the application perhaps. Right now I don't know exact levels required for the VFO signal.

I actually have my own design Si5351 board. It's heavily based on the Adafruit one but also includes buffer devices on each output of the Si5351. It's a smaller PCB also. It's now connected to the ESP32 and also the LED versions of this project and working. The Adafruit PCB will also fit my PCB.

My Si5351 board SCHEMATIC IS here. And a picture of the prototype is here. The BOM is here.

 

Depending upon the facilities you require in your own build, for a particular purpose, you may need to further alter or add to the Sketch provided by TJ.

A PCB ?

I am currently working on a PCB for this project for my install into the FT-7. It will include the ESP32 board socket, plus the other parts required. The actual display will be connected with a short cable, see below.

The PCB arrived on 24th Apri, 2019. I have loaded it up and tested the ESP32, the Display and encoder.

The PCB is 50 x 80mm. NOTE:- it ONLY suits the ESP32 board I purchased, as shown above.

The un-loaded area at the bottom of the PCB is a low pass filter for the output which in the case of the FT-7 is approx. 6MHz filter, so that the output is sinusoidal.

For use in the FT-7, only one output of the Si5351 is required so the other 2 outputs are not used. For other projects though, they could be bought out to header pins fitted into the nearby prototyping area. (lots of pads on 0.1" grid at the end of the PCB.)

 

SCHEMATIC?

24th APRIL, 2019:- This is a draft Schematic. NOTE: It contains some options like TWO different TFT displays (ST7735 controller) which actually connect to the connector "JP3". Some variations for power supplies and also it shows band selection inputs. The actual PCB has some prototyping areas in case of minor changes being required. DRAFT Sch in pdf format

The overlay showing values is here.

There have ben some minor chnages to this PCB and Schematic, which I will detail here soon. eg, the 40M band input pin has been moved to avoid a conflict with port D12 which needs to be at logic "low" level at programming time.

 

Come back later and see how this project has progressed !

vk3pe

 

 

Page created on March 18th 2019, by VK3PE and last updated on May 9, 2019