Ramsey Electronics FM100B Instruction Manual page 10

transmitted over the air.
The whole process of filtering, mixing, and level detecting is repeated in the
left channel as well. This completes the basic analog circuit description of the
FM100B. If you are interested in more detail of how it works, there are many
good books and magazines which deal with circuitry of this sort in smaller
manageable circuits which can help you delve further in what is going on.
MICROCONTOLLER DESCRIPTION
The coding of the microcontroller is mostly set up to simply process the
changing of the frequency and monitoring the VCO voltage. As you will see,
the codes logistics lay out in an easy to follow pattern.
Let's look at a sample code operation. We will start with two given conditions:
- The unit is powered up
- The unit has been set in setup mode. In this state the far right decimal
point is blinking and your frequency may be changed.
1. A user presses the FREQ UP button.
2. The microcontroller stops scanning the LD (Lock Detect) line and sees what
key the user has pressed.
3. It's a Frequency key? Is the unit in setup mode?
4. Yes. Increase the frequency value in RAM by 100 KHz.
5. Send the appropriate divide by N to U2 along with the rest of the required
data.
6. Decode the display digits and update the display for the new frequency.
7. Mute the microphone.
8. Send a confirmation beep to the user.
9. Un-mute the microphone.
10. Wait for key release (if no key release, repeat process from step 4).
11. Continue polling LD and updating status indicators.
We hope all of this information will help you better understand about what is
going on inside the FM100B. This should give you some insight if for some
reason you have assembly troubles or something isn't working properly when
you finish building the unit. Remember most projects like this are made up of
many smaller ones. All you have to do is break them down to understand
them better. Now on to building!!!
FM100B • 10