Having been rather stopped in my tracks from early June for a few weeks due to a knee replacement operation (from which I’m well on the way to recovery), not able to get out much, not able to drive for eight weeks, or mow the lawns or walk very far, I turned my mind to light tasks that I could do sat at a desk or bench. I decided to make a few FM/AM converter PCBs, then came across some rather nice ABS project boxes, which – at 10cms x 6.5 cms x 5cms (4” x 2.75” x 2”) - were a little too small for the PCB that I designed back in July last year.
I therefore re-designed the PCB to reduce its size from the original 10.5cms x 4.5 cms, down to 8cms x 3.5cms, which fits neatly into the ABS box. I mounted the PCB to the underside of the lid on spacers and designed a waterslide ‘decal’ (transfer) to fit the lid. The height of the spacers depends on the type of tactile push-button ‘momentary’ switch used. The switches that I use are fairly generic on ebay, entitled ‘Tactile Switch PCB Push Button Momentary with Coloured Caps 12 x12x 7.3mm’. To correctly space the PCB from the lid when using this type of switch requires four 5mm diam x 10.5mm long spacers, which I tapped 6BA. The push button requires a 12mm diam hole, which I drilled using a step drill (AKA ‘cone drill’). Two 1mm holes are required in the end of the lid for the wire FM & AM aerials - just short lengths of wire.
I’ve made six boxed converters and tested them using the PIC from my own converter, and along with four of the original size built and tested PCBs I’ll be offering them for sale in the appropriate section. I’ve enjoyed building them while I’ve been ‘grounded’ but when life gets back to ‘normal’ it’s surprising how little time there is for hobbies. No wonder I have so many half-completed projects!
By far the simplest way of building the project is with the strip-board layout which featured in the BVWS Bulletin in Summer 2017, but for anyone who might wish to build their own converter and make a PCB for it, the PCB artwork, circuit, component layout and a couple of pictures of the completed PCB are attached. The positive artwork can be used for either positive resist coated UV PCB laminate or the ‘laser printer iron-on’ technique which obviates the need for a UV light box and developer.
The converter is a great little project which performs really well, enabling FM stations to be received on a medium wave AM radio with no connections to the radio, so it's especially ideal for AC/DC 'live chassis' radios such as the Bush DAC90A. All credit to the original designer, Guy Fernando! (Forum member ‘i4cy’). Guy has confirmed to me that he’s still able to supply the programmed PIC necessary to complete the project, from the link below, where the original Summer 2017 BVWS Bulletin article can also be found. The article has full details of the original stripboard layout for those who aren’t geared up for PCB making:
http://www.i4cy.com/m0oox/fm2am/
All of the components can be readily found on ebay from UK and overseas suppliers, including the RDA5807M FM receiver module.
The first pic below shows the component overlay and the reversed positive PCB artwork. If printed onto glossy paper on a laser printer, then ironed onto PCB laminate, it will be the correct way around. There's lots of information on youtube atc about the 'iron-on' technique.
The second pic is of the underside of the PCB showing the correct orientation of the FM module, mounted on solder pins. It also shows the switch and spacers.
The third pic shows the top of the PCB with all the components in place except the programmed PIC from Guy.
The fourth pic shows the PCB mounted inside the lid of the ABS box, and the AM & FM 'aerials' in place - each just 15" or so of wire - red for the AM aerial - black for FM.
The last pic is an angled view of the completed converter.
I hope this might encourage a few more to have a go at building the converter.
I'll add a few more pics in a second post.