FM to AM Converter?

[Bobdger]

Over the weekend, an FM to AM PIC controlled circuit and Vero board build notes was posted on the site. Please can any one remember the title?.
Many thanks.
Bob.

[Nickthedentist]

You're not thinking of of the one in the Bulletin, are you, Bob? (Guy Fernando, pp. 24-26).

[Bobdger]

This may be the answer!!!. I will check tonight. Thanks Bob.

[Station X]

Post #7 in this thread perhaps:-

https://www.vintage-radio.net/forum/...d.php?t=137097

[FIXITNOW]

its also on the web as a project
http://www.i4cy.com/m0oox/fm2am/

[Bobdger]

Thanks everyone that is is the one.
Bob

[Argus25]

I thought I would add to this thread, in case people don't know about these. I only discovered them a couple of years back. There is an excellent quality vintage FM to AM converter made by Audiovox and they are readily available on ebay. They have a super high quality continuous tuning FM tuner made in the typical analog design of the 1970's and 80's FM car radios. They put the received FM stations up on an AM 1400Khz signal (or thereabouts) to feed an AM car radio. Their output simply plugs in series with the antenna wire to the AM radio. They are super compact maybe about 5" by 1". I have attached a photo, and one that was installed in a Triumph TR4 to see the relative size of it compared with an AM radio. It is hard to beat the continuously tunable FM receiver.They can of course be used with any AM radio.

[David G4EBT]

Originally Posted by Argus25

They can of course be used with any AM radio.

As they require direct connection to the radio's aerial socket, not to vintage radios which don't have an aerial socket, often for good reason - in addition to having an internal am aerial, they are AC/DC live chassis so external connects must not be made to the chassis. Some AC/DC sets do have socket for an external aerial and RF earth isolated by capacitors, which these days would need to be Y Class.

The constructional article on the scanning FM/AM radio converter in the Summer BVWS Bulletin has the merit of not requiring any direct connection to the set. It just has two aerials - one to receive the FM signals - the other to transmit it on MW to the adjacent AM receiver so FM on a DAC90A or other live chassis sets isn't a problem. (For the duration of FM transmissions that is - however long that continues, but don't let's go there!).

Given how many threads there have been along the lines of "I've got this Bush DAC90A off eBay and I'd like to rip the insides out and fit a DAB/Bluetooth jobby in it", I imagine that the article will prove quite popular and deservedly so, because not only does it facilitate reception of FM stations on AM only radios, as a constructional project, it overcomes two obstacles which some constructors would otherwise come up against: Namely, though it's PIC-based, programmed pics are available from the author, and secondly, it's built on strip-board so obviates the need for a PCB.

The RX FM modules are cheap too - £2.19 for two post free from a UK ebay supplier.

From my perspective in reading the article, the stripboard layout (Fig 2 on page 25) is rather small and indistinct. Also there is no underside view of where the strips need to be cut or the mounting of the momentary switch used for scanning and setting stations. The close-up on the upperside of the stripboard give little hint of the switch which is hidden on the underside. That won't be a problem for experienced constructors who will sort that out by reference to the circuit, but might baffle or deter inexperience constructors.

Not in any way wanting to sound critical of this ingenious little gizmo - just saying that anyone inexperienced wishing to build it will need to exercise some care and will need to carefully compare the tracks with the circuit to make the necessary nine cuts in the tracks, as explained by the author in the text. The mounting of the FM module on ten tinned wires will call for some care too.

Won't be long I think before we have steady stream of 'success stories' as has been so with the highly popular mini-mod.

Early days, but I think this thread has legs and will run and run!

[Philips210]

Hi.

I am going to build this interesting little circuit and have just ordered the pre-programmed PIC.
Whilst on the subject of PICs, I am looking into purchasing the Microchip PICKit 3 which seems to be a fairly comprehensive programmer. I've seen cheap versions on ebay but it appears these are not the genuine item. I think I'd rather pay the extra for peace of mind. Microchip will give a decent support by all accounts so it seems a false economy buying a counterfeit version. The inexpensive adapter boards which accept the PIC on a ZIF ic socket available on ebay are worth having though.
Any thoughts on members' experience of the PICKit 3?

Regards
Symon

[Argus25]

Originally Posted by David G4EBT

... has the merit of not requiring any direct connection to the set.

It is great that these economical units don't require any direct connection to the set.

I guess for many radios, including transistor radios with internal ferrite antennas there were no external antenna connections commonly either. So the output from an audiovox converter would then be more suited to boosting up a bit and transmitting like a pantry transmitter. The great thing about the audioxox unit is the high quality superhet FM receiver in it.

[Terry_VK5TM]

Originally Posted by Philips210

Any thoughts on members' experience of the PICKit 3?

I run a Pickit3 and have done for a few years now without any problems.

Couple of points though:-

They were temperamental when used with MPlab-X software - not sure if this issue has been fixed (I don't use MPlab-X, I think it's a great pile of )

Clones usually have something in terms of functionality missing, so my choice is the original, even if it costs more.

Terry

[FIXITNOW]

I have a PICKit 3 here at work we use them a lot
nice piece of kit

[David G4EBT]

Originally Posted by Philips210

Whilst on the subject of PICs, I am looking into purchasing the Microchip PICKit 3 which seems to be a fairly comprehensive programmer. I've seen cheap versions on ebay but it appears these are not the genuine item. I think I'd rather pay the extra for peace of mind. Microchip will give a decent support by all accounts so it seems a false economy buying a counterfeit version. The inexpensive adapter boards which accept the PIC on a ZIF ic socket available on ebay are worth having though.
Any thoughts on members' experience of the PICKit 3?

Dave Jones on his EEVBLOG had quite a rant about the PICKit 3 when it was introduce, to such an extent that the makers responded (positively).

Time has moved on and the last of the three links below is probably the most relevant and encouraging:

First review:

https://www.youtube.com/watch?v=vfmLu6XzBtw

Maker's response:

https://www.youtube.com/watch?v=3YUvlrVlNao

Update:

https://www.youtube.com/watch?v=HWlpqSrabKs

Hope they're of interest.

PICs aren't in my skills portfolio - I'm not far enough up the food chain - old dogs/new tricks comes to mind!

Splendid gizmos of course - I've just ordered the pre-programmed PIC, and separately, the RDA5807M FM Radio Module.
(From a UK supplier at the ludicrous price of £2.19 for two with free P&P).

[Philips210]

PICs aren't in my skills portfolio - I'm not far enough up the food chain - old dogs/new tricks comes to mind!

Hi David.

I'm in the same boat and have been putting off having much contact with PICs but feel that I should try to familiarise myself with them so I'm not left out.
Thanks for the links and to everyone that contributed.

Regards
Symon.

EDIT: I've just ordered a PICKit3 and adapter board and hope to experiment with it in due course.

[60 oldjohn]

The mounting of the FM module on ten tinned wires will call for some care too.

Won't be long I think before we have steady stream of 'success stories' as has been so with the highly popular mini-mod.

Early days, but I think this thread has legs and will run and run!

Hi David I will start the ball rolling. I am really pleased with the convertor. I bought the pic already programed from the author. Due to the case mounting holes for the veroboard being different spacing to the circuit I have moved some components to suit.
I managed to ruin two of the FM chips, the solder pads are really fine and break off if the wire is touched in the slightest. I eventually soldered 0.5mm tined wire (offcuts from the other components) onto the veroboard. I applied flux to the solder pads then wedged the chip between the wires. When soldering FM board I had a wet cloth under veroboard to prevent the wire unsoldering and dropping out of the veroboard. Actually only 8 of the wires are used
I am using the convertor with a DAC90 with good results. Around 200m to 270m there is a lot of electrical interference in our house. The MW is a lot clearer 300m + I have set tuned in around 360m. I have noticed that there are two tuning peaks.
I am able to use my DAC 90 as an everyday set now.


Pictures of convertor before boxing up, complete with a lot of interconnecting wires. The unit uses about 22ma and will automatically shut off after 2 hours if no buttons are pressed. I tried buying the two Chokes at Maplins, they only had one value in stock, got it home on my tester and it was not the value it said on the packet. There is a tactile switch mounted under the Vero to switch on, change stations, memorise favourite station at switch on and previous station depending on how long the button is pressed.


I will be watching the post now for a free pre programmed chip from the author !!!!


John.

[Philips210]

Great result John and a vote of confidence for anyone considering building this very useful converter. I am going to build this circuit and recently received the pre programmed PIC. It will probably be a good few weeks before I start construction of the circuit as there are many things on the go at the moment.

Thanks for the warning about the FM module re the vulnerable solder pad connections.

Regards
Symon.

[David G4EBT]

Congratulations on John as the first forum member to 'go public' on the successful completion of the project. Good to know that it's working. John has kindly donated the components to me to make the board, and I've obtained the programmed pic from the author.

Given that it uses 20mA, I wonder why an on/off switch wasn't included, given that the unit won't switch off until 2 hours has elapsed, which might be long after the desired listening period, and needlessly drain the batteries? I wonder if there's any detriment in including an on/off switch?

The FM module 'U2' on the strip-board layout, doesn't actually have the same 0.1"/2.5mm spacing are strip-board or ICs - the five notches span only 8mm rather than 10mm, so as John says, it needs to be mounted on fine wire. Luckily, they're so cheap at £2.19 for two post free from a UK supplier on e-bay, so you get one to mess up with, and one to succeed, hopefully! It's evocative of the old poem about sowing corn: "Four seeds in a row - one for the rook, one for the crow, one to die and one to grow".

I'm not a fan of strip-board, albeit for a simple layout such as this it has some merit and was the method used by the designer. I only discovered the odd spacing of the notches when I set about designing a PCB for the converter, which is at an early stage. Initially, I spaced the notches at 2.5mm then was puzzled to see that the module didn't line up, so I had to adjust the spacing accordingly. I'll mount the module on 1mm veropins. I'm not keen on the board being secured on only two bolts at one each end of one edge of the board and 'swinging free' at the other edge, so I'll be mounting the PCD on four 6BA c/s screws, one at each corner.

The circuit shows no connection to pin 4 of U1, yet on the strip-board layout, there is a wire connected to pin 4, the other end of the wire going to a strip which has no other connections. Seems odd!

John has shown that if built as the strip-board layout shows, the project works fine. Whether or not my PCB layout will work - only time will tell when I've finalised it and built it. I've only done a component overlay at this stage of development, with an 'X-Ray' of the underside track layout. Not thoroughly checked, so it's only attached here for interest - not as a 'good to go' layout.

The second pic shows the FM module - a poor pic, but the solder pad notches can be seen on the right hand side, and from what John says, they're easily dislodged if great care isn't taken.

Who's going to be the next past the finishing line?!!

[Bobdger]

I am still waiting for my fm module!!!. Ordered from china.
Good result John, I will start construction of the circuit as
soon as the fm module arrives.

Bob.

[60 oldjohn]

Hi Bob, I soldered the module in last after soldering all the other parts in. To aid construction I placed (bend contacts but do not solder) an IC holder where the FM chip should be (remember the FM chip is 0.1" or one hole wider than a standard DILL socket). So no reason not to get started!
To get things in perspective I have a photo of the two damaged boards with a dressmakers pin!

As already mentioned I gave up on attaching the wire first to the chip as shown. I finally soldered 0.5mm wires to the veroboard the wires hold the FM board in place while soldering.
I soldered all ten pins, only 8 pins are used.

There are opportunities for a couple of wiring mistakes the photos should be used in conjunction with the circuit.

Good luck every one, John.

[David G4EBT]

Just an update to post #17, for anyone who might wish to go down the PCB route, I've now drawn the PCB artwork for the layout I've devised, which has the correct spacings for vero-pins to mount the FM module. The pads for the switch are to suit the momentary tactile push-button switch that John kindly gave me. It has to be mounted on the underside of the PCB with the tabs bent flat and soldered in place.

As and when I've check the board for errors and etched and built it, I'll add an update.

Meanwhile, it's 'work in progress'!

Hope that's of interest.