Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
Audioguru, when making the pcb design I noticed that the schematic given and pcb layout given are not the same at pin no 2. Supposedly one of 0.0047uF capacitor leg should connect at pin 2 of lm386, but in the pcb layout, it connects to potentiometer. Which one is correct, the schematic or the diagram given?
Many parts connect to ground. Pin 2 of the IC, the 1k pot, the 0.0047uF capacitor and others.
The pcb layout and the schematic are the same. Follow the wiring around the pcb to see.
Hi Kekkaishi,
I think you are making the old version from Electronics Lab that is full of errors.
I looked in Google for Radio Shack Special and found the updated version listed under RSS.
It uses a double-sided pcb with one side used as a ground plane.
The pcb you are making is full of errors.
Audioguru, the new one still didn't connect the pin 2 with one of the capacitor's pin. I'm curious why the capacitor's leg was connected to the potentiometer leg whilts in the schematic , it doesn't show like that.
The 0.0047uF capacitor connects to ground.
The 1k pot also connects to ground.
Pin 2 of the LM386 IC also connects to ground.
Millions of parts also connect to ground.
They are all connected together.
It is very confusing because the IC is on the bottom of the pcb and the other parts are on top (I think).
Audioguru, you said before that the pcb schematic I've shown you on my previous post had many errors but when I try to compare to the one you gave me, I don't see any differences, I mean in term of connections. Just orientation of the component is the difference. So may I know where are the errors?
Actually I want to use tda7000 at first but looking at the number of component, tda7000 needs about 38 component if I'm not mistaken. Therefore, I've decided to use MPF102.
Anyway, if this radio shack don't work, I'll move on to tda7000.
The TDA7000 is obsolete and has not been made for many years. It was replaced by the TDA7088 that is in a tiny surface-mount package and also has very poor performance.
The pcb for the Radio shack Special radio that you have has only one connection for items #19, #23, #24 and #25. The variable resistor #25 does not have a triangle for its 3 wires.
The pcb was changed probably to make it work better.
I've successfully made this radioshack. thank to all who helped me especially Audioguru.
May I know where can I get the information for the working principle of this Radio Shack Special? Right now, I only know that 1K potentiometer is for gain adjustment, 10k for volume control and tuning capacitor is for tuning the frequency. I need more information of this RSS working principal.
Another thing I need to measure the 3-db bandwidth and power for FM radio signal, IF signal and demodulated audio signal using spectrum analyzer. I need some guidance from the experts.
Hi Kekkaishi,
Good, it works.
It is a REGENERATIVE radio. Look for an explanation in Google. It is not a Super-regenerative that automatically sets its sensitivity.
It has an AM detector that detects FM (with distortion) if the circuit is tuned to one side of an FM station and it "slope-detects" the FM because when tuned to one side the signal amplitude increases and decreases (AM) as the FM frequency approaches the tuning peak then moves away from the peak.
A real FM detector ignors AM (static interference) and the high gain IF limiting amplifier removes AM interference.
The bandwidth is narrow at the peak but is wide further down because there is only a single tuned circuit with positive feedback so that it almost oscillates.
A real radio has many tuned circuits and the proper bandwidth is designed in.
So in this Radio Shack Special, I still can measure the 3-db bandwidth and power of FM radio signal, IF signal and demodulated audio signal using spectrum analyzer, right?
I've searched google for spectrum analyzer but I still don't get the way to measure this 3 things. Hope you can guide me or link me to the correct website please. Thank you very much.
That's mean I can only measure for FM radio signal an demodulated audio signal right? For FM radio signal and demodulated, may I know where should I connect the probe of the spectrum analyzer to the Radio Shack component?
A spectrum analyser shows many frequencies. If it is sensitive then it would show all the radio stations and communications devices in its area if it has an antenna.
The Radio Shack Special filters the signals it picks up so its output is only a single amplitude modulated frequency. Then it AM detects to produce audio. A spectrum analyser will show nothing.
If the sensitivity control is turned up too high then the transistor oscillates at the tuned frequency. Then a spectrum analyser would show a single line.
But the circuit is too simple and connecting a spectrum analyser will disrupt the circuit.
Maybe you could use a sweep generator to feed the radio and use a 'scope (not a spectrum analyser) to see the bandwidth. Then you will see a very narrow bandwidth if the sensistivity is set high and the bandwidth will increase as the sensitivity is reduced.
When the bandwidth is too narrow for an FM signal then the output audio will be distorted.
This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
By continuing to use this site, you are consenting to our use of cookies.
