Projects to kill time before Xmas - Ardupilot Mega On Screen Display

This simple On Screen Display uses a board intended for use with a drone or quadcopter. The project was devised by Mike Stevens G7GTN and published in issue 12 of CQ-DATV.

Video quality from the finished item is excellent and ideal for use with amateur TV output. You should understand output is monochrome and single page.

Two PCB's are used in the project but only one is permanently installed, the other is used for programming. Unfortunately there are no mounting points on the OSD board so a little fabrication is required if you plan to box it up. I soldered some push pins to the grounds on mine and soldered the other end of the pins to copper clad board. If you want to run from the shack 13.6v supply a tiny regulator board can be added. See picture.


Out of the packing the OSD board is pre-loaded with a font set suitable for aircraft use e.g. an artificial horizon, not useful for amateur TV. Mike has provided a font set which can be downloaded and installed using the Arduino IDE software and a simple to use terminal programme. All instructions and software links are available on the CQ-DATV site so I will just outline my build.

Before you connect up the board there is a small amount of soldering needed. The OSD board has two isolated sections. At one end video output at 12v and at the other digital input at 5v, the 12v input feeds a 5v regulator which we are told is prone to overheating. For this project the two sections are linked and run with a single 5v supply. There are link points on the board so the alterations are a five minute job with the right tools.

Digital input to the board is serial so the second board you'll need to source is an FTDI USB to Serial interface. These are cheap as chips from eBay; mine was less then £3.00 delivered. Most will come with a set of leads. Beware as some Chinese sellers advertise as FTDI and supply an alternative which in my case didn't work.

Pictured is the genuine board which is only required during programming. Mine can be re-attached if I want to make changes.


Prior to boxing up; the parts cost less than £10 and it worked great. I built two of these with different talkback frequencies; a paged unit is planned using several boards in one enclosure.


OSD with no video input. Monitor TV is under a shelf causing some shading at the top.


Links. Working at time of writing. There are other suppliers for the hardware.

CQ-DATV issue 12.

On-Screen Ardupilot Mega Display MinimOSD Rev. 1.1

FT232RL 3.3V 5.5V FTDI USB to TTL Serial Adapter



Projects to kill time before Xmas - 34.5MHz to 4.4GHz Oscillator

Due to a back problem I've been stuck at home for a while. I already have nuts and bolts in the lower back but now another disc has failed.

That's the best excuse yet for spending time in the shack; but what to do?

There were a few ideas in the BATC magazine which appealed to me and another in the CQ-DATV mag. At the time the ADF4350/1 devices were catching attention and a couple of interesting projects were submitted to CQ-TV. The first was an Arduino controlled ADF4351 development board project submitted by Alain Fort F1CJN. The ADF chips are a wideband synthesizer with Integrated VCO. Developments boards are available on eBay for about £20 at the time of writing.

Alain supplied the C++ code for the project and it was something quite new to me. Reading through the lines there were some similarities to the Basic language I learned back in the early seventies. Initially I bought the Arduino and the 1602 LCD shield. The LCD shield incorporates up/down/left/right and a couple more buttons for enter and reset. Programming the Arduino with Alain's code went smoothly and I was pleased when the LCD lit and displayed the correct menu items.

My ADF4351 board eventually arrived from China and I rigged a breadboard to test it in conjunction with the Arduino. At this point it should be pointed out that a resistive divider is used between the 5v digital signals from the Arduino and the 3.3v input to the ADF4351 board.

Again things went smoothly and I had RF output from the 4351.

Up till this point I hadn't considered housing the boards so started a search for an Arduino enclosure with space for the development board. I was amazed to find there's hardly anything to enclose an Arduino board let alone any extra space. It hadn't occurred to me that people generally use the Arduino for experimentation and therefore don't use posh boxes.

Then I remembered seeing an enclosure when I bought my Pi camera; a push together Perspex box. I wasn't sure it was big enough but ordered one figuring if it wasn't I could use it later for something else. At this point I think a reveal is in order.


Now anyone who knows the 1602 LCD shield will know that the six buttons are recessed some 6mm from the face of the display. At this time the penny dropped and I realised the display can't be fitted in the enclosure. This was confirmed when I found a small packet enclosed containing six buttons and a small PCB upon which to mount them. The only display which would fit is a 1602 serial display.

I'm slightly edgy at this point because it now occurs to me that Alain's code is written for the parallel display only. Anyway it's obvious from the display pictured above that I was able to hack the code and insert serial drivers. There was a slight setback when the I2C address of the display was different to that in the driver pack.

Eventually the ADF4351 board was mounted outboard at the back of the enclosure. It was probably a good thing as it was properly screened in a separate tinplate box.



If I had workshop facilities with pillar drill and metal folding tools I'd love to have a made a decent enclosure; but hey this is a workshop tool with frequency coverage from 34.5Mhz to 4.4GHz and it'll do for me.

You can find detailed information for this project through the BATC


Learning a little C++ with Arduino

For the last three weeks I've been waiting for various components to arrive from China. These are parts I could buy in the UK for twice the price; but patience rules.

Most of the items are for two Arduino projects, a Morse code reader and a wide range oscillator. I had the oscillator working at one point; however the Chinese seller had sent the wrong PCB, one with a smaller frequency range. He refunded the difference but now I have to wait another three weeks or so for the correct board.

Of course now I'm left with a spare ADF4350 development board; but I have an idea so it won't be wasted. These boards are plentiful on eBay and they're based on ADF4350/4351 IC's. The two ranges are 137 MHz to 4.4GHz and 34.5MHz to 4.4GHz.

In some respects the wait has not been a bad thing as it has given me time to play with the EEPROM code. Originally the code for the Morse decoder was written for a parallel LCD; but I wanted to use a serial display because there are fewer wires involved. It appears at the moment to be working but I can't be 100% sure as I'm still waiting a tone decoder IC.

If and when I get these projects finished I'll post some pictures up.

Dabbling with Arduino takes me back to the time I learnt Basic about 37 years ago. I built a motor drive to open and close my bedroom curtains. I had bought a Video Genie computer which if I remember correctly just beat the Sinclair ZX80 onto the market.

What goes around comes around.

Kramer Matrix Switch Swapped Out

In an earlier post I talked about the acquisition of a matrix switch; a Kramer 6x6. At the time I thought it was great; I still do except I've now exceeded input capacity.

Truth is I probably miscalculated at the outset. Anyway I've put the 6x6 up for sale and bought the nice 8x8 pictured below.

These switches are sold as pro video equipment and cost a mint new, a look around your favourite auction site will reveal some real bargains.






DATV Express - All Working Fine

With some trial and error I finally got the DATV Express working well with the Windows software.

In fact during the recent ATV contest weekend it was used without any hang-ups. We (G0WFT/G4CPE/M0SKM) had taken along a Digithin setup as a backup system but it stayed in the car.

When I first acquired the Express board I also bought an Odroid XU4 and tried it with Linux successfully. The only issue was the lack of a compatible capture device; I will revisit Odroid and endeavour to get it working with DATV Express.

DATV Express

On impulse I just bought one of these ready built Digital TV boards. So far I've had it running on 2 metres 125k/Symbols and 23cms 4m/Symbols. Software is available to drive the board in Linux and Windows varieties and I tried both. Windows is easier for me as I'm a Linux numpty.

What I could use is some initial settings to get me started. I was unable to get a satisfactory picture on the 70cm band.

Anyway since it cost me close on £240.00; I decided to house it early on. Here are a couple of pictures.This post will require updates when I get to grips with the board.





2m Band-pass Filter (Another)

This 2 metre BPF was a design I found in the Radio Communications Handbook page 5.30. Having recently committed my existing filter to a breadboard project I decided to go ahead and construct a replacement.All of the critical dimensions are shown in the handbook so construction was quite easy.

Since I completed the filter it has been aligned by a friend Arthur G4CPE. Setup was carried out on Arthur's Wiltron RF Analyser. Bandwidth is 5MHz and loss is under 2dB at 146.5MHz.

This is an inexpensive project using basic tools, coils are wound on a 9.5mm drill bit and the piston capacitors were found on eBay. There's not much to it as you can see from the pictures below.







Breadboard (Real) for 2m Portable DATV

Fed up with assembling my 2m kit for portable ops; I decided to do a proper breadboard job of it. My XYL was issued a spec and duly set off for Morrisons kitchenware department. I'd had a bad back for a while so she didn't moan and came back with a board which was just the right size.

Prior to placing the components I decided that some would fix OK with double sided adhesive pads; heavier ones would be screwed down. It wasn't long before I was reaching for the board packing to see what it was made from as I couldn't get the screws started. Just my luck it was Bamboo and real tough.

Anyhow I wasn't going to be beaten and reached in the cupboard for my Dremel; drilling start holes for every screw. Evidence that the wood is tough can be seen at the front edge where one of the screws snapped off.

There are two items not shown; my DCI filter and class A power amplifier, both too large to mount on the board.

Here's a picture showing how it worked out.


In the black box is a USB programmed SI570 frequency synthesiser which retains the setting when powered down. The oscillator can be detached quite easily and used with my 70cm DigiThin setup.

The MMIC amplifier is run at very low level and has good linearity.

This is the first time I've put something together without a metal box. In this case it seemed entirely appropriate.

My DCI-145-2H Bandpass Filter

Had this filter for a few months now; it was an eBay purchase which I thought was a bit of a gamble. I'd seen it for auction and emailed DCI to find out if it could be retuned to cover 146.5MHz. Of course I should have known what the reply would be. I soon received a polite reply "We would need to get the filter back in order to retune it. The cost would be $300. A new filter would cost $450."  Of course this didn't include any shipping costs so I declined the offer.

Anyway I bit the bullet and bought the filter.

You see I know a man for the job so I tucked the 4lb chunk of metal in my rucksack and took it to see my friend Arthur G4CPE. Arthur did this sort of work for a living and also has the tools for the job; a Wiltron 640 RF Analyser. After a brief look at the performance it appeared in good condition and certainly met the claimed specifications.

At this point I'll introduce the beast to you with a couple of pictures, note the large nuts and bolts on the back. There's no info about these that I could find.




Without futher discussion Arthur asked me to undo the lock nuts central to the four cavitys, having just spent a few quid on the filter I think I uttered in a high pitched voice "Are you sure"?

Knowing Arthur I should not have worried; it couldn't have taken more than five minutes before I was prompted to  do up the lock nuts. While it was not possible to retain the original 2Mhz bandwidth it now covers 146.5MHz and the bandwidth is still only 3.7MHz. Return loss is inside the manufacturers spec.


This filter really is the business; still covering all of the two metre band, I'm using it inline for my two metre RB DATV transmit and receive. One more picture with the marker showing the tiny loss at 146.5MHz.

Important Note.One of the members at my local club says he borrowed one of these filters and there were no adjusters at the back. He could be wrong and it may have been a different model, however please check before buying.








VFO Options for The DigiThin DATV Transmitter

Having just completed my third DigiThin build I decided to try some VFO alternatives. During the first build I had used my  work bench synthesiser; an Si570 based device working up to 950MHz. If you had wondered why anyone would want three DigiThin kits in the first place; there is a simple explanation. Yes two were for me; one intended for permanent install in the shack and the other for portable use on two metres only; I already have another system for 70cm portable. The third was built for a friend and because I enjoy construction so much.

DigiThin kit builders will be aware that Brian G4EWJ included a small snap off section of the PCB for use as a VFO; it seemed a shame not to use it so I decided to go-ahead and give it a test. The only components needed are the Si570 Programmable XO/VCXO of your choice, resistors for a 30dB attenuator and a pull down resistor to hold the Si570 in the off-state. The Si570 I used is the 210MHz CMOS version.

The challenge for me would be installing and running Brian’s software to run the Si570, I know very little about Linux. Anyway I decided not to worry about the software figuring somebody would help. Following assembly of the VFO I powered it up without the pull down resistor and the little board produced some RF; about -20dBm which is roughly what’s required at two metres. At his point I fitted the pull down resistor and tried to make sense of Brian’s instructions for the software.

Cutting to the quick I have to admit I did need help and Brian came to the rescue. In fact I had installed the code correctly but misunderstood and got the command line syntax wrong. It wasn’t very long before I had the VFO under software control and it works very well. To clear up the oscillator harmonics I do pass the signal through a homebrew bandpass filter before applying the RF to the DigiThin modulator.

Here are some pictures showing the VFO attached and the DigiThin remote from the Raspberry Pi. I’ll be keeping the two PCB’s linked by ribbon cable and they’ll go into an enclosure with the filter.

Output from the PA is kept clean with an additional filter which I’ll cover in the next post.








VFO option two is a very neat and low cost solution using a kit from SDR-Kits called a QRP2000 USB-Controlled Synthesizer. The great thing about this module is its ability to retain the last programmed frequency. Again it uses the Si570 so filtering is essential as these devices generate vast amounts of harmonics. With appropriate filtering some of these harmonics can be put to good use, I have used the 210MHz version at 437MHz.

USB driver software is available for Windows XP and Vista/Win 7. I’m running Windows 10 on my Pipo X8 and the Win 7 driver works fine. Control software is USB_SYNTH written by Tom DG8SAQ. All software is available through the SDR-Kits website.

In my opinion this is a great VFO solution if you aren’t keen on implementing the VFO software for the Raspberry Pi. Once the frequency is programmed in using a PC; all you need is a 5 or 12 volt supply and the little board will power up where you left it. There is provision to switch the RF on/off using pin 2 of the Si570.

Some pictures of my SDR-Kits VFO.







Information on the DigiThin project can be found on the BATC forum.