[Variable Capacitor]

Thanks a ton for the response.

Just to double check I am thinking of this correctly:

A wire goes from A to O. Then a wire from O tp the circuit. ( this is connecting them in parrell, or did you mean in series? ). Then a wire from G to the circuit.  This gives me the 220pf?

So I would have only two wires running from the cap to the circuit, not 3, and I would have the 220pf. Is that correct?

Thanks again

PS. Is there a schematic of a variable cap I can find online?  Thanks

[Variable Capacitor]

So is that a wire from O to A and then a wire from A to the circuit and a wire from O to the circuit, and dis-regard G all together?

Sorry, I am new to this!

In my mind I see a wire from A to the circuit and G to the circuit gives me 160

O to the circuit and G to the circuit gives me 60

A to O with a wire from A to the circuit and O to the circuit is 220.


Are these correct or just plain wrong?

Thanks again

[Simple AM receiver]

I am using a transistor from a pack of common NPN-Type switching transistors. I do not have the exact model. The are probably like the MPS2222A transistors.

I swapped out the transistor for another one and got the same voltage readings and same results to the speaker.

I will post more on the other site.... thanks

[Simple AM receiver]

Hey Guru Plz Help,

I built the AM receiver circuit and fed the output to the "'AM Radio Power Amplifier" on the LM386 datasheet. I have everything hooked up except I am not using "ferrite beads" on the output of the LM386.

I actually get a Radio Station around 900AM, but the sound is VERY VERY VERY low!!!

I have the IC at a gain of 50 but I have ti put my ear right next to the speaker to hear it. I tried increasing the gain to 200 but no luck.

I tested the voltages given on the AM receiver schematic at the specified transistors and had the same voltage at every spot except Q3 ©... no idea why!!:

Q1 (b) 1.31V 
Q2 (b) 0.71V 
Q2 © 1.34V
Q3 (b) 0.62V
Q3 © 3.87V  <==== I have around .1 V

Is there anything else I can do to increase the volume or to fix Q3 ©????

Thanks man
-crivoli

[Variable Capacitor]

Can someone please explain the leads of this variable capacitor and how to hook it up?
I have never used one and I want to make sure I get this correct.


Thanks
-crivoli

[Simple AM receiver]

My question is if I build this simple AM receiver and feed the output to the LM386 using a gain of 50, should the output to the speaker be good quality audio?

I saw the datasheet for the LM386 and it shows an "AM Radio Power Amplifier" schematic, but can I use one of the other setups without having to add the "ferrite bead" etc... ?

AM Receiver:
http://www.electronics-lab.com/projects/rf/006/index.html

LM386 datasheet:
http://cache.national.com/ds/LM/LM386.pdf


Thanks a ton
-crivoli

[audioguru, question on preamp/amp]

i believe I solved this problem with your help... Thanks a ton.

I seperated the mic and speaker and I also changed somve values of what I was using.

Please check my other post on a "Simple AM receiver"

Thanks again.

[audioguru, question on preamp/amp]

Question 1:
I built the circuit on the LM386 datasheet with the amp at a gain = 20. Everything works fine.
I then adjusted the gain to 50 and it works correctly.
When I adjust the gain to 200 the speaker just squeals horribly.
I have built this circuit before and used a gain of 200 with no problems. Any idea of what I could be doing wrong?

    LM386 datasheet: http://cache.national.com/ds/LM/LM386.pdf

Queation 2:
I hooked up a preamp circuit using a LM741 and send the output to the amp I built with the LM386. Needless to say the output to the speaker is very bad quality.
Is there anything special I need to do with the output of the preamp before it goes to the input of the audio amp?

I have attached the LM741 preamp schematic

Thanks all
-newb

[FM Transmitter]

I was going to use alligator clips :)  Just wanted to make sure this wouldn't throw anything off.

Thanks again

[FM Transmitter]

The designer of the AM ciruit said he built this on a breadboard.

Any idea how to hook up a variable cap on a breadborad since the connectors don't fit?

[FM Transmitter]

So am I able to replace the coil and tunning capacitor in the schematic with any coil and tunning capacitor I find that are compatable with each other?

Thanks

[FM Transmitter]

So, I could be safe in replacing those components of the schematic with those I found on e-Bay. Does that sound right?

Also, on the transmitter schematic it is not clear of what L1 is:
http://www.electronics-lab.com/projects/rf/011/index.html

Is it another ferrite coil, or magnet copper wire? I assume it is another ferrite coil since this is AM and it's tuning cap is the same value as the other.

thanks again

[FM Transmitter]

audioguru,

No I didn't realize that. How then on that schematic is the antenna a 220uH and the resistor is a 500pf? Do you have to tune the capacitor until it reaches the matching value?

[FM Transmitter]

The AM receiver schematic specifies a 500pf variable capacitor.

The one  on E-bay is 60/160pf. Do you think that will work, or will I need to change values of other coponents on the schematic? 

Thanks

[FM Transmitter]

audioguru:

I appreciate your patience with me.

Would this work for the am receiver as the 220uH component?
http://cgi.ebay.com/Ferrite-Loopstick-Antenna-Coil-Crystal-Radio-Radios_W0QQitemZ6619389741QQcategoryZ7275QQssPageNameZWD1VQQrdZ1QQcmdZViewItem

also I can not seem to find any good variable capacitors..... any suggestions?

thanks man

[FM Transmitter]

I agree it does not specify the range, but this 'should' work in my scenario correct?

I don't want to try them if they are not useful to me. If you think they will work for my project I will give them a shot.

I would builf the receiver first to see if I could get AM stations on it.
Why doesn;t the receiver have an antenna? Is this normal?

Thanks

[FM Transmitter]

audioguru:

I found an AM transmitter and AM receiver on the project page:

http://www.electronics-lab.com/projects/rf/006/index.html  -- Receiver
http://www.electronics-lab.com/projects/rf/011/index.html  -- Transmitter


Would this work in my scenario to send audio through a mic across my house to the speaker?

I thought it looked promising so I figured I would ask.

Thanks again for the help

[FM Transmitter]

Well, I guess I set myself up for that one!!

I have already made the amplifier circuit I wish to send the audio too. I was looking for a simple transmitter/receiver for this project but I am not finding anything.

I guess a 49Mhz walkie talkie schematic may do the trick but they seem impossible to find. Just my luck :(

[FM Transmitter]

Well, seeing as how I am obviously NOT an expert ( yet :) ), is there any practical solution for sending audio wireless to a receiver that I could either make myself or obtain from some other  reasonable source

[FM Transmitter]

I am wanting to transmit voice from a mic to a receiver that would amplify it out of a speaker.

I assume this can be done with a 27MHz signal, am I wrong?

I found some schematic here, can you tell if they work: http://jap.hu/electronic/rf.html

I can't really read them very well...... can you help explain them a little.

Thanks

[FM Transmitter]

I took apart the remote from my sons remote controlled car ( he is 2, and the remote is very basic ). It is a 27MHz remote and I tested the distance and it works very well throught my house.

Shuold I try building a very basic 27 or 49 MHz remote used in RC cars or walkie talkies? I am sure I can find some simple schematic for that?  Any thoughts?

Thanks

[FM Transmitter]

OK, that makes sense. I appreciate all of your great help. I may look into something else to try out with this. I am glad you know what you are talking about :)

Hey, one more thing..... I have seen FM transmitter and receiver IC's.  Could this do the trick for me? If one IC sends the signal and the other IC receives it? And if so could the signal be amplified if it were audio through the LM386?

I found a IC receiver here, is this anythign close to something that could work?

http://www.semiconductors.philips.com/acrobat_download/datasheets/TDA7000_CNV_2.pdf

Just something to think about

Thanks

[FM Transmitter]

Have you ever seen an example schematic for a transmitter/receiver that run off of something other than 88-108?

I am really wanting to make this thing wireless, and with the limitations of IR I don't think that will be possible to use.

Should I pick up a book on RF and get to know it better?

Thanks again

[FM Transmitter]

So you still need to build an FM transmitter for a baby monitor device, but the transmitter is not sending a frequency between 88-108 correct?

I am wondering if this is even worth trying!!  :-\

[FM Transmitter]

So am I understanding this correctly?  You are saying that a radio is pretty much the only thing that should be used as a receiver?

If so, what is a good solution for a wireless intercom, or a baby monitor? Do those run on FM transmitters or some other type of transmitter?

Thanks