Ramsey Electronics Treasure finder TF-1 Instruction Manual page 6

D3 is a zener type diode which accomplishes our regulation task. The power
indicator LED provides a visual display when the circuit is energized.
The local oscillator section of the circuit consists of U1 and its associated
components. This 8 pin chip contains a complete oscillator and mixer circuit.
This amazing little chip takes the place of several functional "blocks" critical
to our metal detector design. Since we will want to be able to slightly adjust
our local oscillator input, we have provided a "varactor" diode tuning circuit in
order to enable us to to change the frequency of our reference. We have
used this particular IC for a few years now for a variety of applications and
are still amazed at how it lends itself to more and more designs.
The oscillator comprised of transistor Q1 and it associated components
(including the search coil) generates our probing magnetic field. Notice that
the search coil is isolated from the rest of the circuit via a length of RG174
mini coaxial cable to provide for more stable measurements.
Components R6 and C10 make up our low pass filter that removes the
unwanted mixer output (the sum of the LO and search coil oscillators) The
difference between the two oscillators is amplified by U2, an audio amplifier
integrated circuit. This IC can provide plenty of power to drive the small
speaker, so we also limited the power for use with the optional earphone by
adding a resistor (R10) in series with the headphone output.
TF-1 COMPONENTS LIST
Sort and "check off" the components in the boxes provided. It's also helpful
to sort the parts into separate containers (egg cartons do nicely) to avoid
confusion while assembling the kit.
RESISTORS AND POTENTIOMETERS
1 2 ohm (red-black-gold) [R9]
3 120 ohm (brown-red-brown) [R2,10,13]
2 270 ohm (red-violet-brown) [R4,8]
2 1K ohm (brown-black-red) [R1,6]
2 10K ohm (brown-black-orange) [R3,5]
1 100K ohm (brown-black-yellow) [R12]
2 PC mount 10K ohm trimmer potentiometer (10K) [R7,11]
CAPACITORS AND INDUCTORS
1 470 pF disc capacitor (labeled 470 or 471) [C19]
2 .0015 uF disc capacitors (labeled .0015 or 1500K) [C5,17]
TF1 • 6