Project
I also used 30-gauge wire wrap wire to connect wires from
the tone generator to the electric microphone on the two-way
radio. To locate the connections for the microphone, you have
to disassemble the receiver and trace the foil pattern. If a tone
isn’t transmitted when you push the transmit button, reverse
the ground and input connections. Connection of the receiver
to the speaker is much easier. All you have to do is locate the
speaker and solder the ground and input leads to it.
Testing
If your receiver doesn’t work the first time, it’s probably because component values are off. Ceramic capacitors
have this dubious distinction, and can be off as much as
20% from their stated value. I strongly suggest that you
use good quality Mylar capacitors instead. If you are stubborn like me and you use ceramic capacitors, measure the
values with a meter, and add capacitors in parallel to get
the correct value. If you don’t have a meter that can read
capacitance, the problem is still easy to fix. Just change
the placement of the wires on the 4017 frequency counter.
For example, if you are having problems with steering,
change pin 5 to either pin 1 or 10 or pin 11 to 9 or 6. If you
are having problems with forward, stop, or reverse, change
pin 10 to either 7 or 1.
If you really want to get your project to work the first
time, I strongly suggest that you pretest
circuits as you build them. It’s rare not to
make a few wiring errors the first time.
I always test circuits as I build them,
and I usually get a project to work the first
time. All you need is a couple of extra
components, three resistors, and three
LEDs. Every time you finish a circuit,
attach the resistor and LED at the output
of each IC. For example, to test the
LM556 oscillator, connect the resistor and
LED to pin 9. It should stay lit continuously. To test the 4017 counter, attach LEDs
to pins 10, 5, and 11, and transmit the
various tones to the counter. You will see
the LEDs light for each tone. They may
not be very bright due to pulsating output, so you may have to turn off the lights
to see them. Next, connect an LED resistor combination to pins 6 and 10 of the
4528. When you transmit the steering
tones, you will see LEDs go on. Since
the signal is no longer pulsating, they
will be very bright. Do the same thing
for the other half of 556 One Shot pin
5. Then test the outputs of the other
4017 counter, pins 2, 7, and 10.
Parts List
Transmitter
U1 — CD4066 Quad Bilateral Switch
U2 — LM555 Timer
C1 — .0047 uF Mylar Capacitor
C2 — .0033 uF Mylar Capacitor
C3 — .0047 uF Mylar Capacitor
C4 — 10 uF 15V Electrolytic Capacitor
C5 — .1 uF Capacitor
R1,R2,R6 — 100K, 5% Resistor
R3 — 10K, 5% Resistor
R4 — 68K, 5% Resistor
R5 — 15K, 5% Resistor
SW1, SW2, SW3 — Normally Open
Momentary Switch
SW4 — Single Pole, Single Throw Switch
Receiver:
U1 — LM324 Quad Operational Amplifier
U2 — LM556 Dual Timer
U3, U7 — CD4017 Decade Counter/Divider
U4 — CD4528 Dual Monostable
Multivibrator
U5 — CD4011 Quad Two Input NAND
Gate
U6 — CD4070 Quad Exclusive Or Gate
Q1,Q2,Q3,Q4 — TIP 122 NPN Power
Transistor or Equivalent
Q5 — 2N3905 PNP Transistor or Equivalent
Q6, Q7 2N2222 NPN Transistor or
Equivalent
C1 — 10 uF 15V Electrolytic Capacitor
C2 — .1 uF Mylar Capacitor
C3,C4,C5,C6 — .1 uF Capacitor
R1, R10, R11, R12, R13, R15, R16 — 1K, 5%
Resistor
R2 — 100 ohm, 5% Resistor
R3, R5 — 10K, 5% Resistor
R4 — 10Meg, 5% Resistor
R6 — 68K, 5% Resistor
R7 — 15K, 5% Resistor
R8, R9, R14 — 1 Meg, 5% Resistor
D1,D2 — 1N914 Diode
RLY1, RLY2 Six Volt Relay with . 5 Amp
Contact
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It bears repeating that the beauty
of building your own radio control
vehicle is that you can modify it to
suit your needs. For example, if you
need speed control you can add extra
logic to the counter and inverter. The
inverter could be made from either a
555 or a 4011. You could also install
headlights, or, if you need more
precise turning, slow the speed of
the turning motor by adding a speed
control unit. There are endless
possibilities. NV
40
SEPTEMBER 2005
