hi friends, i am looking for a schematics for fm receiver. that i can set 1 frequency and it will stay working there. even if i close power and open again. like a if battery finish, it need to stay on where we fix it. thank you.
Find an OLD radio. Before about 1975, radios used mechanical tuning capacitors which did not need power to "remember" a setting.
Pretty much the only possible solution, a mechanical tuning capacitor.
Maybe you should take off the knob after setting the station (or cut the string).
Maybe you should take off the knob after setting the station (or cut the string).
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Potmeter and varicap will also work, but only when the temperature doesn't change too much. If the sound quality isn't critical, a TDA7000 kit will then also do, if those are still sold somewhere.
We used to use three TDA7000 kits in the silence detector of the local radio station here (Haarlem 105). They worked perfectly, but I had taken the precaution to use an NP0 trimmer for coarse tuning and the original varicap only for fine tuning.
We used to use three TDA7000 kits in the silence detector of the local radio station here (Haarlem 105). They worked perfectly, but I had taken the precaution to use an NP0 trimmer for coarse tuning and the original varicap only for fine tuning.
I think most MCU controlled FM tuners remember the last station as long as the backup battery is healthy.
The old radio suggestion is a good one, if you don't mind the size. If you rather want something small and inexpensive with analog controls, search online with the following keyword "DSP Full Band Radio Module". You should find references to the DSPM1 and DSPM2 modules. They have the same system on chip inside, but mechanical mounting and pinouts are different. Documentation is available online. It is a module from China with mechanical tuning control. Just turn the knob to your desired frequency. This module is sometimes installed inside tube radios to make them "work" without doing a electrical restoration, or to add the FM band. A mechanical coupling from the encoder shaft of the module to the dial string is needed.
As alternative, the inexpensive "world radio" receivers from China often use the M6959 chip. The internal M6959 microcontroller does have 3 analog inputs: band switch selector, tuning, and volume control. They keep the tune after you change the batteries. This kind of dollar-store world radio is recognizable because they don't have push buttons or LCD displays, they only have rotary or slide controls. The downside is poor sensitivity and they are prone to frequency drift.
As alternative, the inexpensive "world radio" receivers from China often use the M6959 chip. The internal M6959 microcontroller does have 3 analog inputs: band switch selector, tuning, and volume control. They keep the tune after you change the batteries. This kind of dollar-store world radio is recognizable because they don't have push buttons or LCD displays, they only have rotary or slide controls. The downside is poor sensitivity and they are prone to frequency drift.
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I have one of those DSP modules, but I have not used it. I thought I was getting the "big" one, but I received the "small" one for which there is little documentation / online experience to draw on. I'm not sure the two modules are identical in function. So going that route may be a bit of a crapshoot.
There are small kits in the U.S. $2-3 range that use the HEX3653 FM DSP chip. These work surprisingly well and, best I recall, they retain the last used settings on power down / up. Haven't played with mine in a few years.
HEX3653 Datasheet PDF , Unspecified : FM Radio Receiver Module D.I.Y. Kit (for Advanced Users)
There are small kits in the U.S. $2-3 range that use the HEX3653 FM DSP chip. These work surprisingly well and, best I recall, they retain the last used settings on power down / up. Haven't played with mine in a few years.
HEX3653 Datasheet PDF , Unspecified : FM Radio Receiver Module D.I.Y. Kit (for Advanced Users)
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