transmitter 9v to 3v

[audioguru]

Hi Zach,
I'm glad to help you. I've been there and done that a long time ago and it is fun to refresh.
It is good that you see the big difference in battery life. Reconsider using only two AA battery cells. Their voltage will drop to 2V and your circuits won't work. Three AA cells will start at a little more than 4.5V and end at 3V.

You can use your un-needed 9V batteries on my Stethoscope project here:
https://www.electronics-lab.com/projects/science/019/index.html

I've just finished another low battery voltage project and are making them for family and friends:
https://www.electronics-lab.com/projects/games/003/index.html

Along with another low battery voltage project that I posted:
https://www.electronics-lab.com/projects/science/018/index.html

 

[zachtheterrible]

those are cool projects audioguru :lol:

i made the mistake of making this circuit on veroboard and then hacksawing it off, so now i cant really experiment w/ it (i was sure it would work the first time). but now i know the first rule of electronics (4 me neway) it almost never works the first time (again, thats 4 me :lol: ). ive never had a circuit work the first time. It might be a while b4 i build it again.

oh yeah, is that 27k instead of 22k alright?

 

[audioguru]

Thanks Zach,
Most of my designs work fine every time. Yours will too after a little more experience. I always use Veroboard for my prototypes and sometimes must change a resistor value or add one to make it work even better. Luckily I have many 1/10W resistors from answering machines and clock radios that were killed by lightning. Those tiny resistors can be sqeezed in and 2 put in series to make a 1/4W value that I've run out of.
On my last project I made the circuit first, then took it to the store to match a box to it. Mistake! It didn't quite fit into a nice box. So I re-layouted the Veroboard for my next assembly.

22K or 27K, it won't make much difference (only 1.3 times). They are both nearly 5 times higher than the original 4.7K and the variations (current gain, etc.) between samples of the same transistor number are much higher than only 1.3 times anyway.

 

[zachtheterrible]

hello again :lol:

Duz overdriving an oscillator limit the range?

 

[audioguru]

Hi Zach,
A simple oscillator has its drive uncontrolled. An oscillator oscillates continuousy because it has gain (amplification) and positive feedback. It takes some of its output back to its input, amplifies it, gives that larger signal back to its input, amplifies it even more, etc. It can't amplify more when its transistor "hits the supply rails" when it is saturated (turned-on hard) for a half-cycle and cutoff (not conducting) for the other half cycle. Its output is the largest when the saturation and cutoff timing are symmetrical. Bias for the transistor's base (with 4.7K it is saturated most of the time, with 27K it is more symmetrical) determines its output symmetry.
However, your oscillator has a tuned LC network as its load, so its collector voltage can actually exceed the supply voltage when the transistor is cutoff. Just like a child on a swing. Give a little push (the transistor conducts a small amount) and the swing swings like a pendulum (the tuned LC network also swings) until it is back at the position that you pushed it. Give it another little push and it swings higher. The tuned LC network does too. If the transistor is an RF one with a high gain at FM frequencies, it could be operated in "class-C" where it is cutoff most of the time but has a very large output. Your transistor is a "general-purpose" audio transistor that has hardly any gain at FM frequencies so it can't take advantage of operating in class-C.

 

[zachtheterrible]

Your transistor is a "general-purpose" audio transistor that has hardly any gain at FM frequencies so it can't take advantage of operating in class-C.

really now. what type of transistor do you suggest i get then?

Thanx for the explanation, that helped :lol:

 

[audioguru]

Hi Zach,
I'm not an RF engineer, but I could probably find a good RF transistor. It wouldn't make any difference in your oscillator. An oscillator would need to be designed for it to take advantage of its good RF performance.

It would be a lot easier just to add an RF amplifier made from a "general purpose" transistor.

 

[zachtheterrible]

alrighty than :lol:

i just finished assembling the circuit on cardboard so it is really easy to take parts in n out of it. ill let you know how it goes :lol:

 

[audioguru]

Hi Zach,
What do you use for soldering and desoldering tools? Mine makes moving parts easy.

I have and recommend a Weller temperature-controlled soldering iron. Mine is the simple inexpensive "mechanical" controlled one, and I used the same at work. I found mine in the trash at my very 1st job about 40 years ago and it still works fine. When I found it, its mechanical switch was stuck so I replaced it. It has a good cord (teflon that doesn't burn) but I had to supply my own 24V transformer. I use a 700 degree tip that seems to last forever. I never have to "tin" the tip. With it I always use a damp sponge to clean the tip frequently. The sponge-holder is Weller too.

I also use a good solder-sucker. Mine has a sturdy but lightweight aluminum barrel and a conductive teflon small nozzle. My thumb quickly latches it and when I push its button the solder is gone. It is also nearly 40 years old. I clean it out and lube it every couple of years but have never changed its "O" rings. I don't like using the cheap and huge plastic (static problem?) solder suckers nor that Dry-Wick braided stuff.

Are you going to make a high-power transmitter? Keep looking over your shoulder for the FCC and stay away from a little above 108MHZ or the FAA will visit too!

 

[zachtheterrible]

I have a really nice xytronics temperature controlled soldering station (reeealy nice :lol: ). a friend of mine gave it to me because he didn't need it, along with a bunch of other nice stuff. ill have to look into getting a solder sucker, i always just use the braid stuff, works fine.

oh yeah im gonna make a high power transmitter one of these days. gotta walk before i run though in making this little bug. i thought i had it a little while ago w/ the 9v transmitter which works fine, but then you told me about AA's lasting MUCH longer than a 9v batery, so i am getting closer to finally having a bug that i will be satisfied w/.

FAA, federal aeronautics agency?

btw audioguru, do you have a website?

 

[audioguru]

Hi Zach,
Yeah, maybe I'll setup my own website and charge admission. Maybe with a "VIP" extra price section with naked girls holding my designs. I could also get paid for hits on popup ads. Thanks, a great idea.

How far is your range now?

 

[zachtheterrible]

Yeah, maybe I'll setup my own website and charge admission. Maybe with a "VIP" extra price section with naked girls holding my designs. I could also get paid for hits on popup ads.

heee hee hee haaa haa ho hoo hoo ahahahaha. nice :lol:

wel i havent got a chance to experiment w/ the circuit since i assembled it on the cardboard but the first one that i made, i had a range of about 50 feet or so w/ a piece of junk clock radio. what i am aiming for is about 150 feet because thats the range that i got w/ a 9 volt transmitter

my friend's boyfriend (who is an electronics engineer :lol: ) is hopefully gonna be coming over saturday so maybe he'll help me out a bit. hope he's not just a digital engineer :cry:

 

[audioguru]

Hi Zach,
Certainly the digital engineer can design a powerful FM transmitter. He can start with, say a 10MHz crystal oscillator, and use it to digitally synthesize an FM frequency, with as much power as you want. It would be stable as a rock!
It would be like that digital stereo transmitter that comes from Africa or somewhere, posted by our member, The One.

 

[zachtheterrible]

cool 8) . i just bought two 20MHZ crystals to fiddle around w/ so after i finsih this here bug im gonna build me a nice monster of a transmitter

 

[zachtheterrible]

hey audio. i found another 3v fm trans schematic. download this pdf. it says itll go 300 meters.

its identical to mine, accept for the audio part, the type of transistors used, and the 47k instead of the 22k that im using.

the question that i have is will 2n3904 transistor suffice? Thanx

 

[zachtheterrible]

hello again.

well i got that transmitter that i built on the piece of cardboard working. in my sickening incompetence i connected the oscillator transistor backwards :x . Anyway, i tried a 47k resistor instead of the 22k and gues wut, i get beter range :lol: .

im kind of stuck though because my little clock radio runs on 9v batteries . . . dont have any of those around :cry: . you're right, 9v runs down VERY fast. I'm anxious to see what the range is when i plug in a new 9v.