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
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