The SRF02 is an ultrasonic range
finder that works with a single transducer. Using only one transducer
to both transmit the ultrasonic burst and to receive the echo of the
same, reduces the size of the unit to only 20x24mm. The small size allows
it to be easily incorporated in a tube with a diameter of 25mm.
The SRF02 features both I2C and
a Serial Interface. (see PDF SRF02). The Serial Interface is a standard
TTL level UART format at 9600 baud,1 start, 2 stop and no parity bits,
and may be connected directly to the serial ports on any microcontroller.
Up to 16 SRF02's may be connected together on a single bus, either I2C,
or serial. The measurement rank is about 15cm to 600cm, so the received
results are between 0x08 and 0xFF hexadecimal.
Taking advantage of the “dead”
zone (0x00hex to 0x08hex) allows the direct sending of commands to the
"Host". An ER400TRS module connected to the UART using a Pic
16F877A receives the data stream from the Midi-Stick, converting it
with a serial program routine to midi messages, sending it to PortA,
RA4. To have the ability of sending program- or control change messages,
increases the performer’s possibilities to create and manipulate
sounds. Only two bytes have to be sent to get a result from the SRF02.
The first it is the address (between 0 and 15) and the second is the
command itself. For example 0x00 (address 0), 0x55 (command): Initiates
a new measurement - the result is transmitted automatically from the
SRF02 in microseconds by TX.
To control the sensor and both
push bottoms the circuit uses Pic 16F628A. The Pic has an UART and the
ability for LVP (low voltage programming). IC 74HCT573 is the interface
to the Parallel Port of a PC and is used to program the Pic. The ability
to program the Pic "in circuit" helps greatly in developing
the program. (see programming "in circuit")
Transistor (T1) switches VCC of
the ER400TS (Easy-Radio) and VCC of the 74HC4066. After 5 minutes without
detection of a new measurement the circuit enters "sleep"
mode. This explains the need for the transistor T1. Pressing push bottom
S1 wakes the up. A VARTA rechargeable battery, 4,8V 80mA/H is used for
the circuit. The charging is done with a MAXIM, MAX712. The circuit
is calculated to charge the battery in approximately 3 hours.
