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FM-100 Page 36
17H. Install D1, a 1N4148 type diode (orange glass body with black stripe
on one end). Install it in the same orientation as shown in the parts layout
diagram.
18H. Install U4, the IC with the sticker FM-100 into the socket.If your chip
has a dot or notch, orient as shown in the parts layout diagram. If your chip
has a large “1” on one end, this end is oriented as though it were a notch. It
should be placed at the end of the socket closest to R19. This is the
“brains” of your project, keeping track of all the button presses, the
frequency lock, and the rest of the circuit. Be sure all 20 pins are firmly in
the socket and none are bent under.
19H. Install C37, a 10uF electrolytic capacitor (Check polarity!).
20H. Install Q7, a 2N3904 type transistor. Make sure and mount the flat
side in the same orientation as shown in the parts layout diagram.
Now is another good time to check all of your work for soldering and installation
problems before we move on to the EEPROM circuit.
I. EEPROM
EEPROM is where the operating frequency
last used is stored so that the next time you
power up the unit, it goes right back to that
frequency. It sure beats having to remember
the frequency and have to re-enter it each
time you power it up!
1I. Install R1, a 330 ohm resistor
(orange-orange-brown).
2I. Install R2, a 10K ohm resistor (brown-black-orange).
3I. Install R4, a 330 ohm resistor (orange-orange-brown).
4I. Install C3, a .01uF ceramic capacitor (marked .01, 10n or 103).
5I. Install U1, the X2402 EEPROM IC. Make sure that the notch or dot is
installed in the same orientation as shown in the parts layout diagram.
The resistors in this part of the circuit prevent bus contention when the
microcontroller and the EEPROM are talking back and forth. The EEPROM
uses a two wire serial interface. The data line goes between an input and
output depending if you are writing or reading data from the EEPROM. Since
the microcontroller doesn’t entirely know when the EEPROM is switching
between input and output, we don’t want to drive an output with an output by
accident. The resistors prevent an output from driving another output directly.
Содержание FM-100
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