Friday, 8 December 2017

ICOM718 Digital INterface

PTT circuit

Here is the working ICOM "SEND" or PTT circuit. The PC or Mac is connected to the interface using a serial USB <-> RS232/TTL interface cable - costing just a few pounds on Amazon... The signals output from the adaptor that I bought are 3.3V logic, and there is a 5V power supply. I use the negative logic (active LOW) RTS signal to drive the gate of the BS170 MOSFET, when HIGH the 3.3V turns it on and a LOW level turns it off. The output of the BS170 stage is used to drive the diode input on the 1N35 optocoupler, thus giving an active LOW output to the ICOM SEND (PTT) line.


The Audio circuits have yet to be tested and will be published here later. The box that has been made is shown below, Front and back.

IMG 1639

IMG 1640

The front has a switch which will be used to disable the computer PTT/RTS signal to prevent it being accidentally activated during system set-up, along with volume controls for the IN and OUT audio channels. The back has a cable with USB plug (containing the USB <-> RS232/TTL adaptor), the DIN connector to the ICOM718 (using a custom made cable to the rear ICOM 13 pin Input/Output, a Jack for CV-I control signals and two audio jacks for connections to the soundcard of the PC or Mac (I use a small plug-in USB sound interface).

Monday, 27 November 2017

LATEST Sketches and Libraries

Here is the latest update of my sketches and libraries.


Previous sketches have output HIGH/LOW signals on a one connection on the 4-way jack on the VFO hardware. This signal was coded from D12 to switch the first PA I made from RX (HIGH) to TX (LOW).
The new sketches output active LOW codes on two pins of the 4-way jack, with Arduino UNO connections body=GND, ring=D12, ring=D13, tip=+5V.

These connections were chosen to also support a GPS receiver connection to the box.

For the PA-2 switching D12 is used as the LSB and D13 as the MSB of a two bit binary code. This code is then used as,


HL = TX 40m LPF

LH = TX 30m LPF

LL = TX 20m LPF

The codes are used to switch the three LPFs in the PA-2. And also to switch the Antenna connection from RX to TX.

Sunday, 19 November 2017

Slow build QRP PA-2

I've been at this project for a while. But its slowly coming together. It is a QRP PA (2-3W output) for 40, 30 & 20m. It uses a MMIC pre-built module running on 12-15V, a set of three LPFs and an Arduino Nanocomputer to run things.

It provides TX RX switching and LPF switching from a two bit binary input on the rings of a a 4-way jack (the other connections are body GND & tip +5V. This input is compatible with my VFO output jack- this jack is used for GPS inputs when finding time and Maidenhead Locator, and as a TXRX/band command to the PA running other sketches which generate WSPR, JT65, CW, PSK, RTTY signals.

IMG 1694


The display is simple, just the title "PA, the band big in the middle and TX or RX at the bottom.

Tuesday, 7 November 2017


I just noticed that Elektor has cut it's prices in a sale! The Elektor SDR broad band receiver can now be bought for €30!!! This will tune from 100kHz to over 50MHz using an Si5351 DDS. programmed from an Arduino.

Put this together with an Arduino UNO at around €9, a small OLED display and a rotary encoder for around another €9, and you can build a very decent SDR for less then €50!!!

Check it out.

Screen Shot 2017 11 07 at 11 47 26

I built one, which I use with a low cost 96kHz ADC and HDSDR running on either on my MacBook or a PC.

Screen Shot 2017 11 07 at 11 52 08

Screen Shot 2017 11 07 at 11 56 30

I have put the software on this blog, look for my latest download of my sketches.

Friday, 3 November 2017

Quicky on new FT8 mode

Some slides I have presented to BARS Tech Group

FT 8 001FT 8 002FT 8 004FT 8 005FT 8 006FT 8 007

Thursday, 26 October 2017

Weather station - Failed

I found on the web this project ESP8266 Weather Station by Daniel Eichhorn. It uses an ESP8266 processor and WiFi to download weather from Wunderground and display it on an OELD.

It is wired up like this

Screen Shot 2017 10 26 at 18 06 10

This is the result of the example code they provide working

Screen Shot 2017 10 26 at 17 59 41

Which was great. But the next day when I switched it on, it did not work. I removed everything, re-installed everything on my MacbBook, no go. I installed everything on a different computer (my iMac), no go. I found it would connect to my router and was given an IP, but would not connect to any site on the internet. I have given up. Maybe my router is somehow blocking it??? Tried to check the router but login admin/password does not work, is the router defunct?


Wednesday, 18 October 2017

RS232/TTL conversion for digital interface

What a puzzling world, that of RS232.

RS232 is used for communication with Data Terminal Equipment. It used to be commonly found on the back of Windows PCs in the form of a male DB9 connector. Carrying the following signals

pin    sig
1      DCD
2      RXD input from rest of world ) ICOM CI-V CAT control
3      TXD output to rest of world  )
4      DTR
5      GND PC side ground
6      DSR
7      RTS used for switching to transmit (PTT)
8      CTS
9      RI
The signals on RS232 are anything up to +/-13V, not TTL 0/5V.

Screen Shot 2017 10 17 at 14 24 49

And the logic is inverted. positive logic '1' RS232 HIGH = negative logic '1' TTL LOW voltage. So,for example, a data byte B10101010 on RS232 and TTL look like those above.

To convert RS232 to TTL logic signals means converting the voltage levels and the logic. This is commonly done with an FT232 or MAX232 chip and an opto-converter, like the 1N35 or the better PC900V.

Screen Shot 2017 10 17 at 14 56 33 PC900V

Data Interface

To interface todays PCs with USB input/outputs a further step is needed. To convert USB to RS232. Here is a typical complete circuit using a FT232R IC to generate an islated CI-V interface:

Screen Shot 2017 10 14 at 23 31 01 Cables

Another practical way is to use a low cost, ready made cable which has on one end a slightly larger USB plug, containing the "232" chip, and on the other 6 wires carrying TTL level RS232 signals.