Figures 6 & 7 - Circuit wiring for the transmitter (left) and receiver (right) boards
Wiring for the two boards should look something like the above figures.
' {$STAMP BS2} ' {$PBASIC 2.5} ' MultiButtonTx.bs2 ' Transmit pushbutton states for multiple pushbuttons using the 433 MHz ' RF Transceiver. TxPin PIN 14 TR PIN 15 Baud CON 16468 PbStates VAR Byte HIGH TR ' T/R Line High - Transmit DO PbStates = INA ' Input Pins P3..P0 SEROUT TxPin, Baud, [PbStates] ' Transmit all push button states PAUSE 10 LOOP
' {$STAMP BS2} ' {$PBASIC 2.5} ' MultiButtonRx.bs2 ' Receive pushbutton states using the 433 MHz RF Transceiver and play ' tones based on what's received. RxPin PIN 10 TR PIN 11 Baud CON 16468 PbStates VAR Byte LOW TR ' T/R Line low - receive DO SERIN RxPin, Baud, [PbStates] ' Read all Pushbutton states SELECT PbStates ' Select all Pushbutton states CASE %0001 ' Pushbutton at P0 is pressed GOSUB Play_C ' Execute subroutine Play_C CASE %0010 ' Pushbutton at P1 is pressed GOSUB Play_G ' Execute subroutine Play_G CASE %0100 ' Pushbutton at P2 is pressed GOSUB Play_A ' Execute subroutine Play_A ENDSELECT LOOP Play_C: FREQOUT 4, 500, 2093 RETURN Play_G: FREQOUT 4, 500, 3136 RETURN Play_A: FREQOUT 4, 500, 3520 RETURN
The program MultiButtonTx.bs2 utilizes the SEROUT command to transmit the states of the pushbuttons to the receiver board. The INA argument is what’s called the “Nibble Name” which monitors the states of all devices connected to pins 0-3. Recall that the command DEBUG ? IN3 prints “IN3 = 1” or “IN3 = 0” in the Debug Terminal depending on whether the pushbutton is pressed. So when the command INA is called, it’s really the same as calling IN0, IN1, IN2, IN3. Then, when SEROUT TxPin, Baud, [PbStates] is called; it then sends the state of each pushbutton connected to P0, P1, P2, and P3 to the Parallax 433 MHz RF Transceiver.
The program MultiButtonRx.bs2 utilizes the SEROUT command to receive the states of the pushbuttons from the transmitter board. However, it’s also a bit more complicated, since once the states are received, the program then has to decide what to do. In order to sort each pushbutton state, the program uses a SELECT…CASE command. Once SELECT PbStates is called, the received values of each pushbutton state are loaded into RAM as a byte. However, there are four states that are received.
So how does the BASIC Stamp 2 store these values? The simplest way to analyze how this is done is to read each byte in binary. Since PbStates was defined as a Byte, there are four “spots” for the state of each pushbutton. Remember, binary only stores values as 0’s or 1’s, and 0 is usually denoted as low and 1 as high. So if we assign each “spot” to one pushbutton, the CASE command can be used to execute subroutines based on PbStates’s binary value. The table below shows examples of how the BASIC Stamp will read each pushbutton state based on the binary value it has received. Our program is checking the states of the first three pushbuttons, but the INA command can check the first three pins, if desired.
Binary Value |
Pushbutton Reaction |
%0000 |
No PB Pressed |
%0001 |
PB connected to P0 pressed |
%0010 |
PB connected to P1 pressed |
%0100 |
PB connected to P2 pressed |
%0011 |
PB connected to P0 & P1 pressed |
%0111 |
PB connected to P0, P1 & P2 pressed |
Therefore, by knowing the binary equivalent of each pushbutton being pressed; the CASE command can be used to compare each binary condition to PbStates and execute a subroutine based on that value. In this program, depending on which pushbutton is pressed, a different note will play.