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Measuring Voltages Higher Than Vref - A Practical Example
The first step is to decide what the range of actual voltages will be measured:
Suppose the Low end of expected actual voltage 10 volts, and the High end of the expected actual voltage is 18 volts
Since we realize that applying a voltage to the RC210 higher than the programmed reference voltage will "pin" the meter face, we need
to “scale” the actual voltage. This can be accomplished using either a pair of resistors as a voltage divider, or a variable resistor to get
just a portion of the 18 volts as the maximum value to connect to the ADC input. Using a 5-K pot would be a good choice.
What you want is to have the High end of voltage range (18 volts) to be less than Vref. If Vref is 5.00 volts, you might choose to set the
resistor divider (or variable resistor) to produce 4.5 volts as the “sensor” voltage when the actual voltage is 18 volts.
If we look at the math, we see that 4.5 volts is 18 volts divided by 4 so the “sensor” needs to provide ¼ of the actual voltage. If the
power supply is currently providing 13.8 volts, divide this by 4 to get 3.45 volts. If you are using a variable resistor (as shown in the
Hardware Reference Manual), hookup your “sensor” to the battery, and adjust the pot to produce 3.45 volts on the wiper. This “sensor”
will work fine with the ADC input. If the battery voltage ever gets to 18 volts, the wiper of the pot will see 4.5 volts, below the Vref of 5.0
volts, which is what is desired.
We then need to program the meter face used. For this example, we will use Meter 1 and assume the Voltage Reference Value has
been left at the factory default of 5.00 volts:
2064 1* 1* 250* 1000* 450* 1800*
This programs Meter 1 to use the voltmeter meter face and tells the controller that when the sensor is 2.5 volts, this means the actual
voltage is 10 volts, and when the sensor (ADC input) is 4.5 volts, the actual voltage is 18 volts. Note that each of the calibration points
is the actual measured value multiplied by 100 then rounded to the nearest whole valu
e. This is done because there is no “decimal”
point on the DTMF pad, so the controller assumes that the “real” values are whatever you put in, divided by 100.
Using the above example, you should be able to accommodate just about any external sensor.
Alarm Programming
The RC210 incorporates 5 alarm inputs that can be used to remotely monitor such things as a door open, high temperature of the
repeater PA, etc. Each Input responds to a logic level change, such as going from high-to-low and low-to high (this is known as rising
and falling edge triggering). When enabled (and triggered), each transition will call its own macro to execute.
For example, you could connect Alarm 1 to an over-temperature switch on the repeater's PA heatsink that closes to ground. You could
then program a Macro that turns one of the Logic Outputs on (or off as needed) to select high/low power on the transmitter and speak a
message to let you know. Once the PA cools down to the point that the over-temperature switch opens again, the Alarm would run a
different Macro, place the repeater back into high power and speak another message to let you know.
Or perhaps you want to connect a weather receiver with S.A.M.E. alerts at the repeater. You simply connect the receiver’s S.A.M.E.
decoder
output to an Alarm Input and program a Macro to play a short message (perhaps “Weather Alert”) and also turn on the Aux
Audio Input to which you have the weather receiver’s audio connected. When NOAA sends a S.A.M.E. Alert, you’ll be automatically
notified and hear their broadcast.
Programming Which Macro To Use With An Alarm
As explained earlier, each Alarm Input responds to a change of voltage on its input. For example, if the voltage goes from +5 volts to
ground (this is called
“falling”
), that will trigger the Alarm and call a Macro. If the voltage goes from ground to +5 volts (this is called
“rising”
), that will call a different Macro. As you can see, this allows for great flexibility
To program which Macro should be called for a
falling
transition:
*2101 <Alarm #> <Macro #>
To program which Macro should be called for a
rising
transition:
*2102 <Alarm #> <Macro #>
Examples:
*2101 1 10
Falling Alarm 1 calls Macro 10
*2102 5 2
Rising Alarm 5 calls Macro 2
Summary of Contents for RC210
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