29 April 2011

FT-817 external tuning knob experiment

Time to share a new development in my accessories for FT-817.

Following the suggestion of a keypad owner I investigated a way to implement an external tuning knob that would overcome the limitations of the small radio main dial.

An optical rotary encoder would be the best component for this task, but they tend to be expensive for an experiment and not readily available. (Yes, I know they can be built from stepper motors, but this wanted to be a quick check.)

In my junk box I located a central-zero potentiometer that was in a VCR jog dial control. Left/right with a spring taking it back to midpoint. I wired it to the analog-to-digital converter of an ATmega168 and successfully controlled the VFO frequency as if I was turning slow/fast the main dial.
Implemented transfer function, with a central no-action range

If one was to further develop this accessory, the most interesting part would be to define a transfer function between the pot position and the VFO change: both step and update delay can be computed to implement a slow-to-fast tuning. For this first experiment I simply used a linear transfer function giving steps in the 130-1300 Hz range.

This kind of interface requires the microcontroller to have an analog-to-digital converter onboard, so one of the ATmega series used in my Frequency Readers. The ATtiny2313 is not suitable for this option unless I get to use a proper quadrature optical encoder (not planning to invest on it).
If you have a spare central-zero potentiometer and ATmega48/88/168 laying around I can send over a diagram and the compiled firmware.

18 April 2011

White on blue Interactive Frequency Reader

Please meet my completed I.F.R. with a white on blue display.

Size is 12cm high, 9cm wide and 3cm thick.

The connector on the left goes to the CAT port on FT817. The jumper is provided to add an off-board on/off switch. On the back of the board there is a resistive trimmer to adjust display contrast (drill a hole in the case). Another jumper (under the LCD) gives access to backlight intensity control.

The pictured object is for sale, including keypad, white-on-blue LCD, molded cable to FT-817. It carries the latest fully featured IFR firmware (including 6 LO values for transverter users). Chips, display and keypad are detachable. It needs a housing.

15 April 2011

My own second IFR build

I built a second "prototype" of the Interactive Frequency Reader on a 12x5 cm perfboard slice. I hope that showing it to interested builders will give a glimpse of the build (non?)complexity.

First of all, here is how it looks like when assembled and ready for usage. Display on top, keypad on bottom, as shown in the previous post schematic assembly diagram.

The display this time is white on blue, very charming. It does require backlight 100% of the time, increasing the current consumption to 32mA.

Noteworthy is that the backlight diode Anode-Cathode is reversed as compared to my other black/green LCD: always, always check your display pinout before soldering it in!

Display and keypad are connected to the board with 2.54mm pin header rows, so that it is easier to remove them for maintenance or re-programming the ATmega168.
Here you can see the actual position of these connectors on the topmost and lowest rows.

CAT cable enters on the mid-left 4-way connector, which is equipped with an old-fashioned jumper if the future owner wants to insert an on/off switch.
And the third picture exposes the board backside. The 10kR resistive trimmer is used for contrast control.

Many connections can be kept short if some building tricks are adopted, like keeping close display and ATmega or using resistor leads to join PCF8574 to the keypad connector.

One useful mod would be to add a backlight intensity control (100R fixed + 100R variable would do).

I am trying to take a decent photograph of the lit LCD. but I need to work on ambient light a bit more. Stay visually tuned!

12 April 2011

I.F.R. suggested layout

If you are going to build the Interactive Frequency Reader on a 12x5 cm perfboard (like the one shipped in the bag of parts), this is a suggested layout of chips, keypad and LCD: keypad on the lowest row, LCD on the topmost row.

Following these positions you will be able to hide all components under the large keypad and display, plus they will be aligned to each other and most wirings will be easier too (pictures will follow). For example some LCD<->ATmega will be straight bridges, and resistors leads will be long enough to connect the keypad to the PCF8574.

05 April 2011

I.F.R. bag-of-parts on offer with molded connector

As announced few days ago, I got hold of a small stock of cables terminated in a MiniDIN8 connector, suitable for FT817 ACC port. So I have assembled an offer for a bag-of-parts bringing to you both the ready-made cable and the fully featured I.F.R. firmware.

04 April 2011

Modding PLL MC145106

Original configuration
 Back to my Pearce Simpson device, I have decided to go through all the steps necessary to make it "digitally" tuneable.

In order to set free the 2x4008 I had to unscrew the front panel and remove all knobs. The black plastic can be removed and the front panel structure detached.

Chips are now exposed. This is "old" technology, so with a solder wick and a thin tip I could set 4008 free just with 3 lifted pads.

2x 4008 on their new sockets
It took a bit of work to get the new sockets in, and they are not perfectly aligned to the board, but the melt solder did the rest and joined everything (checked).

As a final check I plugged in the replacement ICs, connected a dummy load and a frequency counter and made sure that it tunes around.

Next is to draw a board that holds an ATtiny2313 for tuning up and down, AND to make sure that it all fits inside the case before melting any other solder! Oh, yes, I have one more cut trace to restore.