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AM/FM Transmitter Pair

A pair of Altoids-tin sized transmitters, designed to be a cheap way to get music to an old device with no audio input.

rjpope42Rjpope42
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I like old tube radios, and I was disappointed with the options for AM transmitters to get a new music signal to them. The expensive ones were expensice, and the cheap ones didn't work. So I found a schematic online that actually worked, and built a transmitter around it. I intend to make it a very simple, cheap kit, and will make all the files public, because open source.

After seeing this http://hackaday.com/2014/07/30/a-dead-simple-well-constructed-fm-transmitter/ , I decided to make an FM board also, to make them a pair, because why not.

This project serves a simple, cheap, effective way to get an audio signal to a radio.

===============STATUS===============

AM Status - 

Version 1.0 - Arrived with no plated holes, guess OSH park can only handle 1 drill file, oops... drilled the holes myself, got useful prototype info and poof that it works

Version 1.2 - Much better, fixed some layout issues, need to increase pad spacing for the inductors and make life easier by getting a upward facing switch.  When using 9V battery, there is a hum that is eliminated by touching ground (either crystal case or linear regulator heatsink).  Need to troubleshoot.

FM Status - 

Version 1.0 - Designed and layed out on a 9V size rectangle.  Boards are in house and waiting for components to build.

===============FEATURES==============

AM Features -

- choice between 9V and 12V power source

- 5V USB port for powering phone/ipod (only works on 12V power)

- Indicator LED, intended to get brighter with tuning. Seems to be more of a status, considering removal or changing to purely a power indicator

- Antenna out, connect an antenna for limited range broadcast (3' is the scope of the project, enough to sit at your desk, not intended to broadcast from your attic to your basement)

- Line out, feeds antenna through capicitor so you can clip a line directly to your radios antenna, in my opinion the most useful part of this as it allows a simple audio conversion from ipod to AM radio

- Fits in an Altoids tin

FM Features -

- Antenna out, range not yet determined

- Line out, same as AM

- Footprint of a 9V battery

  • FM Transmitter Update 2014-8-17

    Rjpope42 • 08/17/2014 at 15:46 • 0 comments

    The FM Transmitter boards arrived!

    Parts should arrive today or tomorrow, I'll post results of how well it works

  • FM Transmitter Update

    Rjpope42 • 08/13/2014 at 02:59 • 0 comments

    Boards are in the mail, should be here soon!

  • Second Project Log - Features

    Rjpope42 • 08/10/2014 at 14:23 • 0 comments

    A current list of the features, as with the status this will be updated in the details.

    AM features - 

    - choice between 9V and 12V power source

    - 5V USB port for powering phone/ipod (only works on 12V power)

    - Indicator LED, intended to get brighter with tuning.  Seems to be more of a status, considering removal or changing to purely a power indicator

    - Antenna out, connect an antenna for limited range broadcast (3' is the scope of the project, enough to sit at your desk, not intended to broadcast from your attic to your basement)

    - Line out, feeds antenna through capicitor so you can clip a line directly to your radios antenna, in my opinion the most useful part of this as it allows a simple audio conversion from ipod to AM radio

    - Fits in an Altoids tin

    FM features - 

    - Antenna out, range not yet determined

    - Line out, same as AM

    - Footprint of a 9V battery

  • First Project Log - Status

    Rjpope42 • 08/10/2014 at 14:14 • 0 comments

    Created the project, I put the status in this log and the details, and as I post status updates in the log I will keep it updated in the details.

    AM status -

    Version 1.0 - Arrived with no plated holes, guess OSH park can only handle 1 drill file, oops... drilled the holes myself, got useful prototype info and poof that it works

    Version 1.2 - Much better, fixed some layout issues, need to increase pad spacing for the inductors and make life easier by getting a upward facing switch. When using 9V battery, there is a hum that is eliminated by touching ground (either crystal case or linear regulator heatsink). Need to troubleshoot.

    FM Status -

    Version 1.0 - Designed and layed out on a 9V size rectangle, board should arrive the week of August 10th, 2014. Unsure if I will change the layout size to match that of the AM board.

View all 4 project logs

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Discussions

theinventor wrote 01/24/2015 at 07:59 • point

Would you upload greater scheme of AM transmitter, the values of the elements are not visible. Thank you

  Are you sure? yes | no

Rjpope42 wrote 01/27/2015 at 17:18 • point

it's been awhile since I worked on this, I couldn't actually find the schematic, but I think all the capacitor values are uF with the exception of the variable 1-50pf and 470 pf

you can also read some component values off the pictures of the AM transmitter itself

everythinhg else looked readable, I'll try to dig up the files sometime soon

  Are you sure? yes | no

LWATCDR wrote 01/16/2015 at 21:41 • point

Have you thought about this http://en.wikipedia.org/wiki/Carrier_current combine that with DTFM or psk31 and you could have a simple home automation style system.

  Are you sure? yes | no

Rjpope42 wrote 08/12/2014 at 02:38 • point
Thanks for the video link, it's a great explanation of the theory, and I'm glad you like the project!

  Are you sure? yes | no

davedarko wrote 08/11/2014 at 20:53 • point
Neat project! I would be interested in a video and schematics :) I want to put a video here, that I think was featured on hackaday.com before. It gave me a better understanding of AM/FM and therefore triggered an interest in radio transmissions and could be interesting for others. https://www.youtube.com/watch?v=gfz1FbIOMbs

  Are you sure? yes | no

davedarko wrote 08/11/2014 at 20:53 • point
wow, I'm tired, found the schematics :)

  Are you sure? yes | no

ucasano wrote 01/10/2015 at 08:31 • point

where did you find schematics?

  Are you sure? yes | no

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