(Forget all ZN414/YS414/MK414 or 415 etc etc…. Make your own ZN414 or
Mk414 Equivalent Circuit)
Hello Friends, here is a Tested
and trusted mini Pocket sized AM Receiver circuit diagram for you. It’s a
suitable project for fun and Hobby. The most importantly it works great as I
have made it for my own. It can be operated as low as 3volt DC using two AAA
sized pencil batteries. It can receive Medium Wave frequency range from 500KHz
to near about 1100KHz. As a hobbyist I tried to make such a mini AM receiver
for last many years. Like all beginners I too started with simple Crystal Radio
set. But from my experience for last many years and several trials, “Crystal Sets” will only works fine if you are near around couple of
kilometers from your local radio stations and also there should not any high
voltage electrical line passing nearby you. Other wise it’s a waste of time
to trying to receive MW signals from a Crystal
I have gone through number of sites for a working schematic diagram but
you know all are wasted until you got a ZN 414 or MK484 or TA7642 ICs which are
nearly rare to most places and are quite expensive too. If you find one of them
then I think you are lucky.
So I just got a schematic diagram
which is equivalent to those AM receiver ics. This circuit contains 3 BC548
transistors, 3 Resistors and a capacitor and trust me it works fine.
The Front End Detector circuit equivalent to
ZN414,YS414, MK484 or TA7642
Here, All 3 transistors are BC
548;
R1,
R3 ----- 10KΩ;
R2 ------ 270KΩ;
C1 ------ 330PF (Coded as 331 ceramic
type)
Following are the images of my Designed Circuit of the above
schematic.
This circuit is Equivalent to all ZN414, MK484, YS414
or TA7642
Now come to the main Schematic,
Here is the schematic for head phone
Here is the schematic to drive a Loud Speaker
Here points A,B and C are the Points to Equivalent circuits
mentioned above…….
Here is the circuit if you want to add the front end
detector circuit on the same board.
Components List:
Transistors
Q4 ------BC337 or BC549;
Q5------BC548;
Resistors
R4 ---- 1 KΩ;
R5 ---- 100 KΩ;
R6 ---- 680 KΩ;
R7 ---- 3.3 KΩ;
R8 ---- 220 KΩ;
R9 ---- 1.5 KΩ;
R10 --- 10 KΩ Volume Control;
R11 ---- 5KΩ preset;(for adjusting whistling noises if you are gone with the second or third schematic, i.e.
driving an 8Ω _0.25W speaker through an amplifier IC TDA7231. )
R12 ---- 47Ω;
Capacitors
C2
---- 0.47 µf (coded as 474, ceramic or polyester );
C3 ---- 0.1 µf
(coded as 104, ceramic or polyester);
C4 ---- 0.1 µf
(coded as 104, ceramic or polyester);
 |
| 2J Variable Capacitor |
C5 ---- 500 PF Variable Capacitor
or 2J Gang Capacitor found in old
transistor radio;
C6 ---- 100µf electrolytic;
C7 ---- 0.1 µf
(coded as 104, ceramic or polyester);
C8 ---- 0.1 µf
(coded as 104, ceramic or polyester);
C9 ---- 1 µf
or 2.2µf or 4.7µmf electrolytic;
C10 --- 47µf
electrolytic;
C11 --- 220µf
electrolytic;
C12 --- 100µf
electrolytic;
C13 --- .01 uf ceramic ( coded as 103)
C13 --- .01 uf ceramic ( coded as 103)
Diodes D1 and D2 are IN4148;
 |
| Image of IN4148 Diode |
 |
| IN4148 Diode Compare to IN4001Diode |
IC TDA 7231 is 8 pin DIP and can be
operated at lowest 3Volt DC.
L1 ---- Medium Wave Antenna Coil.
with Ferrite rod.
L1 can be made by yourself at home,
take a ferrite rod of 1cm in diameter and 5 to 6 cm long , wind a coil about 80
to 90 turns closely and tightly to each
other with a 30 or 32 gauge enameled copper wire, fix the coil on the rod by a
cello tape.
 |
| Home made MW Antenna Coil. This coil is on flat bar shaped ferrite rod of 5.5cm long and 1.2cm width and the thickness is 0.5cm. |
 |
| Home made Medium Wave Antenna Coil on a former to fit 1cm diameter ferrite rod |
 |
Finished Board /All components on PCB including the
front end detector circuit (the small one above the blue capacitor) mentioned
earlier.
|
 |
Complete Receiver set in a plastic box
|
Points to be noted in making the receiver:
As I told you
earlier it is a tested circuit diagram and will definitely work if you connect
all components properly with correct values. I will prefer to fit the
components on PCB rather than Vero board or testing board. A single loose
connection may not work the kit properly so take extra attention during
soldering.
The circuit may
not work if any one of the semiconductor component i.e. the transistors, diodes
or the IC is faulty. So test all these semiconductors before using. [In IC TDA7231, all 4 pins i.e. pin no’s 5 to
8 are already short circuited from the manufacturer, as they are for grounded
so do not consider it as its fault. ]
For better
performance, always maintain a distance between the MW antenna coil from the
Loud speaker as the magnetic field of the magnet present in the loud speaker
highly effects the receiving signals and make loud noise. Use magnetic field
shielded Loud speakers.
 |
| Magnetic field unshielded Loud speaker |
 |
| Magnetic field shielded Loud speaker |
Regarding to the use of Variable capacitor or
Gang capacitor,
You may find different sized from different old receivers.
Generally you can find a small sized in old scrap pocket radios which are about
250PF to 450PF. Here you need 500PF or more which picture is shown above. But
still if you can’t find the bigger one, you can use a smaller one. For the
smaller one work, you have to attach an extra 100PF (coded as 101) or 220PF
(coded as 221) or 330PF (coded as 331) capacitor parallel to the variable
capacitor depending on the value of the variable capacitor to increase the
value of the variable capacitor (this is an experimental work, that’s up to
you).
 |
Picture of different sized variable or gang capacitors
|
 |
Here CX is the additional capacitor to increase the
value of the variable capacitor C5 the total capacitance of the two capacitors
is CX+C5
|
I hope these points will help you in making the project and wish you luck .
Thanks..........
