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Adding an LED display to an FM radio kit?

Tim01

Dec 11, 2017
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Hi folks, I'm very new to DIY electronics and just learning, but enjoying myself so far! I have successfully assembled a few beginner kits, including an Elenco FM radio kit. It works great, but I thought as a next step to make it even more useful, I might add a very simple LED or LCD screen to display the current station.

I'm honestly not sure where to start, though. The thing about these kits is that they are very "paint by numbers," so I have something that works, but I'm not really sure how or why it works!

Things I'm wondering:

Is this even possible with this kit?
What kind of screen is appropriate for this kit?
Where do I pull a value to display on the screen? I have a sneaking suspicion it will come from the IC somehow, but I honestly don't know.

Here's a picture of the schematic:
File Dec 10, 7 12 21 PM.jpeg

There's a picture of the board itself on Amazon:
https://www.amazon.com/Elenco-FM-88K-FM-Radio-Kit/dp/B004YHZE0G/ref=cm_cr_arp_d_product_top?ie=UTF8

Any other general tips on working with displays are appreciated, too - I'm a complete beginner!
 
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Audioguru

Sep 24, 2016
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I can buy a finished radio with that TDA7088 circuit at The Dollar Store for $1.00 and it comes with earphones and a battery so the radio is free. It works poorly. It is overloaded by strong local stations and cannot pickup weak distant stations that better radios receive perfectly. Its scanning misses many stations but scanning is a nuisance anyway.

If you connect a complicated counter circuit to the radio then the added capacitance and inductance will stop the radio from working.
 

Tim01

Dec 11, 2017
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The kit works well enough for what it is - a beginner learning project. I get lots of local stations with a strong signal, so it's not awful.

I honestly can't tell if you're ragging on the radio for being kinda crappy (honestly, for this purpose, who cares?) or if it literally will not be able to handle any sort of display.

If it's the latter, I'll find another option for learning to work with displays. If it's the former, could you point me to some helpful resources?
 
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Audioguru

Sep 24, 2016
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I learned how to solder so many years ago that I can't remember what I did next to learn about electronics. I think I learned the basics of electronics in school and from magazines then learned the details in university.
 

Harald Kapp

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The TDA7088 doesn't lend itself easily to adding a display.

I found these instructions using an ATMEGA controller, unfortunately these are in German :(
You can also tap into the TDA7088's IF oscillator output and conenct a frequency counter, e.g. the SC3610 which can account for teh required offset between IF frequency and tuned frequency. This page in Cyrillic shows how it's done. Note that they use a PA22429 instead of the TDA7088, but the principle is the same (it sems the PS22429 is compatible to the TDA7088).
 

Tim01

Dec 11, 2017
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The TDA7088 doesn't lend itself easily to adding a display.

I found these instructions using an ATMEGA controller, unfortunately these are in German :(

Ah, if only I had continued my German studies... Aber, mein Deutsch ist ganz schlecht!

You can also tap into the TDA7088's IF oscillator output and conenct a frequency counter, e.g. the SC3610 which can account for teh required offset between IF frequency and tuned frequency. This page in Cyrillic shows how it's done. Note that they use a PA22429 instead of the TDA7088, but the principle is the same (it sems the PS22429 is compatible to the TDA7088).

Actually, this fits with my initial hunches on how it might work from reading the kit's description of the frequency scanning. Can't read a lick of Cyrillic, but maybe I can figure it out with the schematic.

This is helpful, thank you!
 

Audioguru

Sep 24, 2016
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Where can anybody buy that Chinese frequency counter IC that is made for radios? Digikey and Newark know nothing about it.
 

Tim01

Dec 11, 2017
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If you mean the SC3610, I see at least one seller on eBay for a bare chip. I also see a few sellers with control boards and displays for it. Doesn't appear to be super common, but it's out there.

More interestingly, I found a complete kit that uses it: https://www.banggood.com/DIY-FM-Rad...?rmmds=category&ID=233514182&cur_warehouse=CN

The Type 2 option ships with the SC3610 unsoldered, and the entire kit is less than US$10. Very tempted to get it. Looks like a fun kit that does what I'm trying to do, and would be a chance to try surface mount soldering.
 
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