TDA7000 receiver project

[audioguru]

Hi Zach,
The FM broadcast band is at VHF, not UHF nor microwave frequencies, so the rods must be long (1/4 wavelength) to work well. These high frequencies travel along the surface of a conductor so magnet wire doesn't have much surface area, and what's going to hold it up?
If you want very good sensitivity, a yagi antenna (multiple rods) is as big as a car! For FM at home, I have a "rabbit ears" antenna that is almost as long as my outstretched arms.

 

[-=GST=- Nemisis (cs/cz)]

can u not just rip one off some other recive if u have one lying around?? i am making a TDA7000 soon too and i am hoping to use that is it ok??

 

[-=GST=- Nemisis (cs/cz)]

Hi Zach,
He says (I couldn't find the datasheet) that the TDA7000 works with a supply voltage from 2.0V (worn-out two alkaline cells), to 10V which is a brand new 9V alkaline battery.
Have you ever seen the small size of the cells inside a 9V battery? They surely won't last long. Compare the size (and spec's) of those tiny cells with AAA or AA cells. Two AA cells aren't much bigger than a 9V battery but will last at least 6 times longer, and are cheaper. Your choice.

I don't like 9V batteries anymore, I'm designing thingys for 3V now.
Have you seen this one?:
https://www.electronics-lab.com/projects/science/018/index.html

i got a data sheet, its 4.5v-10v

 

[zachtheterrible]

alrighty than :lol: thanx everyone

 

[audioguru]

Hi Zach,
I did find a Philips datasheet on page 2 of Google. Even Philips' website doesn't have it anymore.
It says that their TDA7000 will operate with a supply voltage from 2.7V to 10V. So you can't use only two 1.5V cells. Its spec's are tested with 4.5V and it will also work well at 6V. The LM386 works down to 4V, so maybe four AA cells (4.4V pretty dead to 6.6V new) would be a good choice to power this radio.

Zach, are you using Philips' recommended PCB layout?

 

[zachtheterrible]

Thanx audioguru, i was just about to look up the supply voltage of lm386 cuz i forgot it. i think i may try a different amp because it would be perfect if i could run the whole thing off 2 AA's or AAA's. Could u recommend an amp that will run off that kind of low voltage?

No I'm not using philips pcb, in fact, im not using a pcb. i'm using veroboard. i know, i know, i should do pcb, but i haven't looked into that yet, and i want to build this thing asap :lol: . ive built other high frequency things on veroboard and they always work great.

Oh yeah, i was told that i should have a 100uf decoupling cap on the pwr supply. The schematic calls for 2 .01uf decoupling caps. would the 100uf replace the .01 caps?

Thank you

 

[audioguru]

Hi Zach,
Even though the TDA7000 will operate with a supply voltage down to 2.7V, it won't meet its spec's at that low voltage. The reason I said that you cannot use two cells (3V) is that, and the fact that a 3V battery will drop below 2.7V very soon. Figure that a worn-out cell is 1.0 to 1.1V when loaded. So use 3 or 4 AA cells. AAA cells are a ripoff I guess because nobody uses them.

I have attached the datasheet for the MC34119 small power amp that works from 2.0V to 16V and doesn't need a big output cap.

Even with Veroboard you can keep with Philips' plan by using ground and power busses at each side of the IC for the caps to connect to. Make cuts at all unused track length.

The two 0.001uF ceramic caps (Harry's circuit shows two 1n0 caps at pin 16) decouple the supply very well at radio frequencies. An electrolytic or metalized-plastic cap is lousy, just an inductor. The 100uF or more cap is needed at audio frequencies, without it when the batteries get a little worn, your radio will probably sound like a motor-boat. The 3 caps are wired in parallel. Make sure that your transmitter has two 1nF ceramic caps across its supply too.
I hope that you didn't get any other caps values mixed-up when you translated from nF to uF.

 

[zachtheterrible]

As always audioguru, you hit the nail on the head

I hope that you didn't get any other caps values mixed-up when you translated from nF to uF.

Nope, i just forgot what the values were and didnt feel like looking up the schematic :lol:

Too late to use any layouts. I already have about half the thing done. But I am making it as small as possible, so I'm sure it'll be fine.

If I'm going 2 use 4 AA's, i guess that ill just stick with my lm386. The output cap is not biggie, I found a very small one on a radio that i had.

Question: I asked harry on his website if I need that cap on pin 13, and he said that i don't as long as the antenna doesn't short to anything. Would the antenna shorting to anything mean a ruined circuit?

 

[audioguru]

Hi Zach,
Pin 13 of the TDA7000 is the input to transistors inside. If it shorted to the positive battery terminal (the 2nd rod of Harry's antenna), or to the negative battery terminal (the common of your headphones), then the IC might be damaged. Use the 180p cap.

 

[zachtheterrible]

right then :lol:

 

[zachtheterrible]

Uno question: I wanna be able to use this receiver to the full capability while being able to walk around with it (so i want the antenna to be as big as it should be). Would i be able to put the two lengths of antenna down my sleeves? or would my body mess things up? Also, would i have to hold my arms out like an airplane?

Lastly, i am going to use speaker wire like nigel said and peel it. I would imagine that the part that has not been peeled apart would act like a ribbon cable, or coax, so that I can have a 2 or 3 feet of wire running to the two dipoles. is this true?

btw, i was able to get a click n static when i turned my little transmitter on and off right next to the receiver, so i know its working!! of course i dont have an antenna yet :wink:

thanx :lol:

 

[audioguru]

Hi Zach,
If you want long range then you can't go anywhere near or between the antennas.

Try just a foot or two of ordinary wire for antennas on the transmitter and receiver. You won't notice any difference until their range-limit is reached. It will be a nuisance to keep those huge dipoles stretched and facing each other, and if they are not then their range will probably be worse than simple wire antennas.

Let us know the range of communication with simple antennas and a new battery in the transmitter (it isn't regulated).

 

[zachtheterrible]

alright audioguru, i will do that, and thanx :lol: . gotta wait till tomorrow to go to radioshack and get some wire n junk

 

[dustinpruente]

i have a tda 7000 at home that my dad bought a long time a go and it is just sitting. i never so much as touched it. can someone send me a full schematic on how to make a fm radio with non-crystal tuning. i really dont like crystal tuning. thanks.

 

[audioguru]

Hi Dustin,
Google links to many TDA7000 projects. The IC needs only a single-gang variable cap for tuning. Zach is building this one:

 

[zachtheterrible]

FINALLY!!!! We just had a storm and it sent the stupid fone lines for a loop for a little less than a week, and i haven't been able to post.

Well, i finished the circuit. I found out that the LM386 circuit was crap, or else i am doing it wrong. I think it is overdriven because it makes A TON of noise and oscillates n stuff. But then i figured out i'd just connect it to my computer speakers until i make myself a decent amp, and that works just fine.

This picture is EXACTLY how i have my circuit put together, and I just want to make sure that I haven't done anything wrong.

So did i put it together correctly? Also, will the mute feature make me not be able to hear very weak signals? I've still gotta mess with the LC values, but ill let you know when ive got it working. :lol: Oh yeah, and on this other picture here, I only see 1 antenna, i thought its supposed to be a dipole??

 

[zachtheterrible]

Progress!!!! I got the LC values right, and have it tuned to the FM band. The thing is, I believe that the mute feature is indeed screwing up the receiver because I can only get one station, and I think that that station is located near to my house. I need to know how to disable it :lol: . I also picked up my FM transmitter flawlessly.

 

[John Sorensen]

Congratulations!

j.

 

[audioguru]

Hi Zach,
That's great! You've built yourself an FM radio!

Where did you get its schematic? It differs a bit from the datasheet. The datasheet shows a 10K resistor for R1, yours is 22K. With 10K, the muting is supposed to be disabled. Disconnect R1 with the switch that they show, and it mutes. It reads backwards, but that's what they say.
The datasheet also shows a 10nF cap connected very close to pin 5 and the coil, to ground. Add one, it might help it to work better.
Your value for C15 sets it correctly for the North American de-emphasis response curve.

Speaking about datasheets, did you make the LM386 amp exactly according to its datasheet? Some people leave out the very important series RC network at its output. Without that network and a high impedance load or no load, it is guaranteed to oscillate.

 

[zachtheterrible]

Haa haa, i didnt realize until now that the receiver from the data sheet, and that one from harry's website are one in the same :lol: . I will try the 10k muting disabler resistor. On Harry's, it is a 22k. I will also try the 10nf @ pin 5.

I've got to fiddle around a bit more with the LM386. I didn't want to deal with that because then I wouldn't be sure if it was my receiver or amplifier that was acting up :lol: .

The picture in black is one that i made with SWCADIII. I wasn't sure if I connected the LC circuit correctly so I made that picture to verify.

Oh yeah, and lastly, what is the North American de-empasis respnse curve??

Thx so much :lol: