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Old 17th Jun 2017, 3:56 pm   #21
Philips210
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Default Re: FM to AM Converter?

Excellent, thanks David for going to the trouble of producing the PCB artwork. I will build my converter using your PCB layout rather than stripboard. I have all the components now but can't start this for a while and in the meantime I'll sort out the PCB etching.

Regards
Symon.
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Old 17th Jun 2017, 4:54 pm   #22
60 oldjohn
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Default Re: FM to AM Converter?

When David gets the PCB produced it should save the need for extra jump links up to 20 joints less. Also less chances to make mistakes.


John.
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Old 8th Jul 2017, 9:49 am   #23
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Default Re: FM to AM Converter?

Just an update Pic and fm module have arrived unit built on Vero board up and running good results. See photograph. Now to build my next unit, I will try Davids PCB layout. David have you got this as a Gerber?.
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Old 8th Jul 2017, 2:45 pm   #24
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Default Re: FM to AM Converter?

Well done Bob, another success. I added a 40pf cap across the tuning cap to get the output to 360mtrs, there were some distant stations around 320mtrs where it was previously set at.

I just need someone to work out how to switch it into standby without waiting 2 hours, hopefully with a momentary switch.

John.
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Old 8th Jul 2017, 5:21 pm   #25
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Default Re: FM to AM Converter?

Quote:
Originally Posted by Bobdger View Post
Now to build my next unit, I will try David's PCB layout. David have you got this as a Gerber?.
Firstly, congrats on successfully building the project on strip-board as per the original. That's going to be the best and simplest option for most constructors unless they're geared up for making PCBs. Whenever I can, I prefer to design and make PCBs for my projects as I dislike other methods of construction such as strip-board and Manhattan, but they're perfectly valid means of construction, used with success by untold thousands the world over, so I'm not knocking them.

No - Bob, sorry - I don't have 'Gerber files' for the PCB artwork.

I'm a simple soul - I draw all my PCB layouts using MS PAINT, then I copy and paste as many images as will fit onto one sheet. I print a test copy onto paper to ensure that the image size is exactly as required, adjusting the size as need be in Photoshop. When I'm happy with that, I print the artwork onto 'microporous film for inkjet' to create the mask. I've had little success with normal OHP film.

I'd just like to emphasise that though I can't personally see any errors in the layout that I've created, I haven't actually built the project, so do please check it carefully if you intend to use it. I've etched a PCB and as the FM module is peculiarly terminated with notches, which are not on a 0.25mm (0.1") spaced grid it seemed to me that the best way to mount the module would be on correctly spaced 1mm Veropins so that the module would slide down the pins to lay flat on the PCB, where the notches could then be soldered to the pins.

I've attached a pic of a prototype PCB that I've etched, though the space between the two rows of pins was slightly too small. It might look OK and it was 'OK' but I was brought up to believe that 'OK' is not OK' - things have to be right, so that board has been scrapped, but the attached pic will at least give an idea of how I intend to mount the module on pins. I've attached a pic of the module with the pinouts annotated as there are no marking on it which makes that clear, but I'm sure constructors will - like John and Bob - have sussed it out from the picture of the strip-board layout.

I've since adjusted the artwork and have exposed and developed another board. I haven't yet etched it, but the spacing now looks fine. I've attached the updated artwork, and if anyone would like it (ride at your own risk!), please drop me a PM with your e-mail and I'll happily forward it. (I'm sorry that due to other commitments, I'm not in a position to supply PCBs).

The pics below are:

1) Updated artwork to adjust spacing of U2 pins.
2) Picture of FM Module to show how Veropins will fit the soldering notches of the module.
3) FM Module pinouts.
4) Component overlay of PCB.

Hope that helps.

When I've had chance to etch the updated board and build the project, I'll update the thread.

Every success to other builders.
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Old 8th Jul 2017, 5:44 pm   #26
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Default Re: FM to AM Converter?

There's an image to gerber converter here: https://sourceforge.net/projects/ima...rberconverter/.

I've never had the need to get boards made but from a quick look at this program it seems that the different elements need to be different colours. The tracks are already black so you'd have to colour in the holes something other that the white background colour for it to detect them.
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Old 8th Jul 2017, 7:23 pm   #27
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Default Re: FM to AM Converter?

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Originally Posted by 60 oldjohn View Post
I just need someone to work out how to switch it into standby without waiting 2 hours, hopefully with a momentary switch.
Yes, that's very valid John. Given that it draws 20mA, rather than each times it's used - sometimes for maybe no more than say half an hour - it does seem a needless drain on the batteries for the device to continue to be on for two hours after first switched on before it then automatically switches itself off. I don't know enough about PICs to know whether it would in some way be detrimental to simply add an on/off switch to just switch it off manually before it gets to the end of the 2-Hr session. I can't imagine that it would, but it would be nice to get confirmation from someone a bit 'further up the food chain'. (If my knowledge of PICs was any lower, I'd need watering - not feeding! )
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Old 8th Jul 2017, 7:30 pm   #28
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Default Re: FM to AM Converter?

Seeing that this design applies modulation directly to a free-running oscillator, I wonder if anyone's measured the width of the sidebands?

My experience is that trying to directly AM an oscillator leads to a worrying degree of FM/phase-modulation and it gets horribly worse as you approach 100% modulation.

We're not supposed to operate unlicensed medium-wave transmitters; those of us that do are surely obliged to ensure we do so in the least-intrusive of ways, just as in the 1920s and 1930s it was seen as a sin to operate the then-ubiquitous regenerative-detector in free-oscillating mode and so mess-up reception for your neighbours.
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Old 8th Jul 2017, 9:50 pm   #29
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Default Re: FM to AM Converter?

I cant think of any reason why fitting an On-Off switch would cause a problem for the PIC, it's none different that changing the batteries.
It's what I would try and have the 2 hour limit as a back up in case I forgot to turn it off.

Frank
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Old 9th Jul 2017, 8:02 am   #30
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Default Re: FM to AM Converter?

Another built and up and running.

I followed the tip of soldering the FM module wires to the veroboard first. Tricky job soldering them to the module though.

Colin
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Old 9th Jul 2017, 10:03 am   #31
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Default Re: FM to AM Converter?

Quote:
Originally Posted by FRANK.C View Post
I cant think of any reason why fitting an On-Off switch would cause a problem for the PIC, it's none different that changing the batteries.
It's what I would try and have the 2 hour limit as a back up in case I forgot to turn it off.
I was thinking more about putting it into stand by briefly pressing a switch, possibly the same as the two hour timer does. I expect it is possible for one of the forum experts to come up with a circuit. If not I will use an on off switch as suggested.

John.
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Old 9th Jul 2017, 10:33 am   #32
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Default Re: FM to AM Converter?

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Originally Posted by camallison View Post
I followed the tip of soldering the FM module wires to the veroboard first. Tricky job soldering them to the module though.
I put some flux on a cotton bud and just dabbed it on the edge of the board catching both sides of the PCB at the same time, before wedging it between the ten wires. Then put a wet kitchen towel on the Veroboard to stop the solder melting and the wire dropping out. I soldered the chip in with the boards vertical so had to devise a way to keep the wet towel in position. I applied heat to the short pins then a small amount of solder to the pin and it ran around the pin and onto both sides of the chips PCB. There are 10 pins but only 8 are used. Might be worth practicing on these two pins first. The pin spacing are close, less then 0.1" Veroboard. As already said the PCB pads are very fine, wont take a lot of heat and wires one attached should not be moved. I ruined two of the modules practicing. If anyone manages to ruin theirs I have some the FM modules to spare, for the cost of postage.

John.
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Old 9th Jul 2017, 10:55 am   #33
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Default Re: FM to AM Converter?

Quote:
Originally Posted by G6Tanuki View Post
We're not supposed to operate unlicensed medium-wave transmitters; those of us that do are surely obliged to ensure we do so in the least-intrusive of ways, just as in the 1920s and 1930s it was seen as a sin to operate the then-ubiquitous regenerative-detector in free-oscillating mode and so mess-up reception for your neighbours.
I have done no tests other than the transmission range which is less than about 8 feet in free air. I don't have any nearby neighbours, but it would be interesting to know what if any unwanted un wanted noise is being emitted.

John.
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Old 9th Jul 2017, 11:05 am   #34
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Lightbulb Re: FM to AM Converter?

Quote:
Originally Posted by G6Tanuki View Post
Seeing that this design applies modulation directly to a free-running oscillator, I wonder if anyone's measured the width of the sidebands?

My experience is that trying to directly AM an oscillator leads to a worrying degree of FM/phase-modulation and it gets horribly worse as you approach 100% modulation.
Quite agree. And should be easy enough to do, just use a good frequency counter, measure frequency with the supply voltage to the oscillator at nominal; at 90% below nominal; and at 90% above nominal, so basically simulating modulation trough and peak. Hopefully the frequency will change by at most 100Hz.
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Old 9th Jul 2017, 4:14 pm   #35
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Default Re: FM to AM Converter?

Does the FM module remember the last frequency? If so a simple on/off switch will do.
Does PC shutdown leave the module in a remembering state? If so a manual shutdown button will be a good addition.

Mind you at only 20mA and AA cells being 2000mAh that's 100 hours of "unuse" or use a wall wart.
 
Old 9th Jul 2017, 6:35 pm   #36
Philips210
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Default Re: FM to AM Converter?

Hi.

I have just got mine working and I'm very pleased with it.
I used David's PCB layout and found during construction there's a pad missing in the artwork, this relates to the RHS of the 150uH choke. After checking everything through, I powered the converter but couldn't get it to work. After some head scratching and worries as to whether the PIC was duff, they were luckily unfounded. The problem turned out to be due to the BC184L transistor. The PCB layout is actually for a BC184 (ebc leadout) and not a BC184L (bce leadout). I replaced the BC184L with a BC184 and success!
I also agree about having a switch to help save battery life.
Thanks to David for his PCB layout which is much neater than the stripboard design.
Attached a pic of the completed board.

Regards
Symon.
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Old 9th Jul 2017, 6:53 pm   #37
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Default Re: FM to AM Converter?

Hi

Regarding the FM module, I soldered lengths of 24 SWG tinned copper wire to the 10 pads taking great care not to bend the wires close to the solder pads to prevent the connections from breaking away from the module

The converter's AM output is 950kHz (approx 315 metres) and the output power is quite low as over 6 feet from the radio then nothing can be heard so I don't envisage any interference problems with the neighbours equipment.

Regards
Symon.
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Old 9th Jul 2017, 11:11 pm   #38
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Default Re: FM to AM Converter?

Quote:
Originally Posted by Philips210 View Post
I have just got mine working and I'm very pleased with it.
I used David's PCB layout and found during construction there's a pad missing in the artwork, this relates to the RHS of the 150uH choke. After checking everything through, I powered the converter but couldn't get it to work. After some head scratching and worries as to whether the PIC was duff, they were luckily unfounded. The problem turned out to be due to the BC184L transistor. The PCB layout is actually for a BC184 (ebc leadout) and not a BC184L (bce leadout). I replaced the BC184L with a BC184 and success! Thanks to David for his PCB layout which is much neater than the stripboard design.
Well done to Symon on another successful build!

Thanks so much for 'Beta testing' my PCB layout and for highlighting the missing pad to the RH of Li - the 150uH choke, and for making clear that the pad layout for TR1 is for a BC184 - not a BC184L. I've amended the track layout to add the missing pad, and have marked on the component overlay which pads are EBC, noting that constructors using the layout will need to make sure that whatever transistor they use, the pinouts will need to conform to the pads and the lead-out wires adjusted accordingly.

Thanks for your valued feedback and apologies for any hassles caused. I'm reassured that in other respects, the layout is correct. As I've said, I've yet to build mine due to other commitments so have been unable to verify the layout. The updated artwork is attached, also the negative and positive masks for anyone wishing to make a PCB.

Just one other point to mention: I added four solder pads for the momentary switch to suit the one that John ('60 oldjohn' that is) kindly gave me, but made them quite large so that other similar switches can hopefully be accommodated. The switch is of course mounted on the track side of the PCB - not the component side. (The same as it is with the strip-board layout).

Every success to other prospective builders - the tricky bit is clearly the mounting of the FM module, but at under £2.00 each post free in the UK, or five for £2.00 post free from China, it's really no drama if anyone jiggers up the module trying to make soldered connections to the whacky notches!

Happy to forward the artwork by e-mail to anyone who wishes to PM me.

Have fun!
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Old 10th Jul 2017, 12:06 am   #39
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Default Re: FM to AM Converter?

Quote:
Originally Posted by David G4EBT View Post
Thanks for your valued feedback and apologies for any hassles caused.
Hi David.

That's OK and it wasn't too much problem finding the cause of the problem. I somehow just went straight to it as I remember being caught in a similar way many years ago when repairing a TV, I think it may have been a Thorn set using a BC183L transistor.

Quote:
Just one other point to mention: I added four solder pads for the momentary switch to suit the one that John ('60 oldjohn' that is) kindly gave me, but made them quite large so that other similar switches can hopefully be accommodated. The switch is of course mounted on the track side of the PCB - not the component side. (The same as it is with the strip-board layout).
I had quite a few different tactile switches available. I bent the tags so they were roughly flush with the underside of the switch housing, it's now effectively a surface mount switch. Before soldering the switch to the board I had to trim a very small amount off each leadout as the leads were slightly overlapping the solder pads.

Regards
Symon.
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Old 17th Jul 2017, 6:12 pm   #40
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Default Re: FM to AM Converter?

I guess that I'm not alone in saying that I found the circuit diagram in the Bulletin indistinct and had to use a magnifying glass to read it, and to enlarge it when printing. I've therefore re-drawn the circuit for my own convenience and have attached it in case it might be of help to other constructors. (I still haven't had change to build it!). I've attached it as a PDF which might help.

Every success to anyone who is building the converter or who intends to!
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