Remote Control of Icom IC-PW1 Amplifier
The first commercial solid state ham radio amplifiers came to the market already in eighties. For fifteen or twenty years their prices were high and tube amplifiers continued dominating. Only quite recently has there been a trend towards solid state. My first solid state amplifier was a TenTec Hercules II that I used in nineties. It served me well until I begun building somewhat bigger tube amplifiers. In DXing every dB counts, you see. My next solid state amplifier was and still is an Icom IC-2KL. It has proven to be a reliable work horse for remote use. Only once did it's automatic tuner AT-500 have a smallish hickup when gears got stuck. Lubricating gears before trouble comes might be a good idea. My next solid state amplifier was not an obvious choise.
In Europe the dominating manufacturer is SPE with it's Expert line of amplifiers. I thought about buying either Expert 1.3 KFA or Expert 2KFA. Ameritron ALS-1200S was also an option to be considered. It's basic structure seems solid and straight forward. Acom had announced Acom 1200S, but for some reason it took far too long for the amplifier to actually come to the shops. I had already waited for years that Elecraft would produce it's announced 1500 watt amplifier. Well, they did deliver - but only 500 watts. Also Yaesu had demonstrated a very sleek full gallon amplifier. That product was discontinued before birth. Of the actually existing amplifiers the fourth to consider was Icom IC-PW1. It is conservatively constructed, it's cooling is done better than just about anything that is available in Europe. The bad point of IC-PW1 is that it is not made for remote use. Firstly, just to switch it on requires physically pressing a button. Secondly, there is no longer a voltage controlled band interface available at all which dictates using software control. Which leads to the third obstacle, Icom's CI-V interface has bus collision problems. These problems can be solved, however, so finally I bought a used IC-PW1.
At first, I thought that I would simply connect remote controlled relays in parallel to the push buttons of IC-PW1's control unit. Due to it's miniaturized mechanical design, like having surface mounted components all around, I abandoned that plan very quickly. It would have been far too likely to break the control unit if I tried to solder anything inside of it. I had earlier done some experiments with solenoids that pushed buttons of a radio, so I knew that it would be fairly easy to implement remote control using push solenoids and an Arduino micro controller. JA3OOK had done pretty similar a thing using servo motors and another type of a micro controller. The schematic diagram of my remote control system is below.
The easiest way to have feedback of what is going on at the remote end would have been simply to use a web camera pointed at the control unit of the amplifier. Instead, to save some network bandwidth I used photo transistors to observe the LEDs of the control unit. To get a power on-off-indication I added one photo transistor to look at a meter light. I had to add some aluminum here and there to avoid stray light causing wrong indications. There remote reading of meter values as I thought that functionality to be unnecessary. It would have been easy to add photo couplers to meter leads and then read meter values using Arduino.
The only difficulties in this project were mechanical ones. The photo below shows how I arranged the photo transistors close enough to the LEDs. Due to the solenoids taking so much space some of the photo transistors had to be installed hanging on some extra leads through holes in the aluminum box. This can be seen in the left side of the aluminum box. Wires connected to the diodes are cut and have loose ends in the picture as the photo was taken when rerouting these wires. The final assembly is somewhat different.
There are two types of software in this remote control system.
Firstly, Arduino micro controller code is written in C style programming language and it is embedded into the micro controller. Basically, it is a timer controlled infinite loop that reads photo transistor voltages via analog inputs, and if there is a change in any value, the program sends all analog input values to a Windows computer via a USB port that behaves like an ordinary COM port. The loop also listens text based commands from the Windows computer via the same USB port. There are commands to make the solenoids push the buttons of the PW1 control unit, a command to ask status of all analog inputs, and a test command that basically only tests that the micro controller and the Windows PC can communicate. The commands and other data are in clear text format so one can fully control the amplifier using any serial port communication program.
That is not a user friendly way so in addition there is a Windows program written in Visual Basic that implements a simple user interface to control the amplifier. This program looks as shown below.
It is a simple event driven Windows program. If one presses a button the program sends a command to the micro controller and reads and interpretes a response message, if any. There is only one small trick to make the system a bit more robust. Controlled by a timer, once in a while the control program tries to read status messages. If there is one available then obviously the micro controller has informed about a manually commanded band change or some other event that is not control software initiated. In addition, every now and then a status inquiry command is send to the micro controller. This is done just in case there has been some error related to earlier status checks.
There was some honing to choose timer values so that the user interface is smooth enough and simultaenously one does not loose any messages due to port communications related time-outs. Interrupt driven status message handling would obviously have been more elaborate, but basically this crude implementation works well enough.
In principle this amplifier should be able to change bands automatically when connected to an ICOM radio. However, I never managed to get it work. The amplifier and my ICOM IC-756PRO did handshake just as written in the user manual and by looking at the signals using an oscilloscope I would say that all should be fine. Except that the amplifier never followed the radio. In any case, this amplifier was intended to replace a ICOM IC-2KL that uses ICOM's old band data voltage system. That's why I included band data voltage functionality to this control system. It is shown as Band Follows Radio button in the user interface.