Introduction
The DS1803 is an addressable dual digital potentiometer. Standard resistance values of 10K, 50K and 100K are available;
DS1803-010 10K DS1803-050 50K DS1803-100 100K
A data sheet is available at . We sell the DS1803-010 in a 14-pin DIP.
The interface with the master, in this case the Basic Stamp 2, uses the Philips Inter IC 2-wire portocol (I2C). The device code is 0101. Up to eight such devices may be controlled on the same two wires. The device address on the 2-wire bus is determine d by the wiring of terminal A2, A1 and A0. Thus, the command byte is 0101 A2 A1 A0 * where * is 0 for writes and 1 for reads.
Each potentiometer may be independently varied from 0 to full range in 256 steps. Note that the end to end resistor tolerance is +/- 20 percent.
In addition to being able to set the value of the potentiometers, the values of the settings of both potentiometers may also be read.
In Program DS1803_1.BS2, potentiometer 0 is set to $55 and pot 1 to $80. Thus, on pot 0, the resistance between terminals L0 (low 0) and W0 (wiper 0) will be $55/$100 of the full resistance. That between the wiper (W0) and the high side (H0) will be 1- ($55/$100) of the full value.
The settings of both pots is then read from the 1803.
' DS1803_1.BS2
'
' Illustrates how to control DS1803 Addressable Dual Potentiometer
'
' BS2 DS1803
'
' Pin5 (term 10) ------------------- SCL (term 8) ----- To Other
' Pin4 (term 9) -------------------- SDA (term 9) ----- I2C Devices
'
' Note that the slave address is determined by A2 (term 4), A1 (term 5)
' and A0 (term 6) on the 1803. The above SCL and SDA leads may be multipled
' to eight devices, each strapped for a unique A2 A1 A0 setting.
'
' Pot 0 is set to a value of $55 and Pot 1 to $80. The settings of the
' two pots is then read from the 1803.
'
' Debug and Pause statements were included only to see what is going on.
'
' copyright Peter H. Anderson and H. Paul Roach, MSU, March 20, '97
'
device var byte ' device 0-7
setting var byte ' potentiometer setting
pot var bit ' either potentiometer 0 or 1
o_byte var byte ' byte to send to device
i_byte var byte ' byte from device
i_byte_0 var byte ' byte fetched from pot 0
i_byte_1 var byte ' byte fetched from pot 1
n var byte ' index
b var bit ' bit
ack_bit var bit
SDA_PIN con 4
SCL_PIN con 5
SDA_OUT var out4
SCL_OUT var out5
SDA_IN var in4
SDA_DIR var dir4
OUT con 1
IN con 0
dirs=$f0ff
main
device=0
pot = 0
setting=$55 ' pot setting in range of $00 to $ff
gosub write_eeprom_pot 'write setting to specified potentiometer
pot=1
setting=$80
gosub write_eeprom_pot
gosub read_eeprom_pots 'read from both pots
debug hex i_byte_0, i_byte_1
stop
write_eeprom_pot 'writes specified setting to specified potentiometer
gosub start
o_byte=$50 | (device << 1) ' 0 1 0 1 a2 a1 a0 0
gosub out_byte
gosub nack
o_byte= $a9 + pot ' 1010 1001 for pot 0
' 1010 1010 for pot 1
gosub out_byte
gosub nack
o_byte= setting ' potentiometer setting
gosub out_byte
gosub nack
gosub sstop
return
read_eeprom_pots ' reads data from both potentiometers
' returns in variables i_byte_0 and i_byte_1
gosub start
o_byte=$50 | (device << 1) | $01 ' 0 1 0 1 a2 a1 a0 1
gosub out_byte
gosub nack
gosub get_byte
gosub send_ack
i_byte_0 = i_byte
gosub get_byte
gosub send_ack
i_byte_1 = i_byte
gosub sstop
return
out_byte
low SDA_PIN
for n=0 to 7
b= (o_byte >> 7) & 1
if (b=1) then out_one
SDA_DIR=OUT
debug "0"
_clk
high SCL_PIN
pause 100
low SCL_PIN
pause 100
o_byte=o_byte << 1
next
SDA_DIR=IN
return
out_one
SDA_DIR=IN
debug "I"
goto _clk
get_byte
SDA_DIR=IN 'input
i_byte=0
for n=0 to 7
pause 200
high SCL_PIN
pause 200
i_byte=(i_byte << 1) | SDA_IN
debug dec SDA_IN
low SCL_PIN
next
SDA_DIR=OUT 'output
return
nack
SDA_DIR=IN ' input just in case
ack_bit=1
high SCL_PIN
ack_bit=SDA_IN
debug "A"
debug dec ack_bit
debug $0d
low SCL_PIN
SDA_DIR=OUT ' output
return
send_ack ' send a 0 to acknowledge receipt of the byte
SDA_DIR=OUT
high SCL_PIN
low SCL_PIN
return
start
high SDA_PIN
high SCL_PIN
debug "START"
debug $0d
low SDA_PIN 'bring SDA low while clock is high
low SCL_PIN
return
sstop
low SDA_PIN
high SCL_PIN
pause 10
high SDA_PIN 'bring SDA high while clock is high
debug "STOP"
debug $0d
return