dlp-io8-g

Python code to control the DLP-IO8-G USB-to-TTL device.

The DLP-IO8-G is a simple USB data acquisition module which permits to receive or send TTL signals on 8 lines using a very simple serial protocol. It relies on the FTDI VCP driver which is present in the standard Linux kernel so that there is not need to install any driver: it works out of the box.

From a software point of view, it appears as a serial device which can be controlled by writing and reading characters.

For example, the following Python code, switches all data lines to 0, then 1, then 0 again, with half second delays.

    from serial import Serial
    from time import sleep
    
    dlp = Serial(port='/dev/ttyUSB0', baudrate=115200)  # open serial port

    dlp.write(b'QWERTYUI')  # sets all lines to '0'
    sleep(0.5)
    dlp.write(b'12345678')  # sets all lines to '1'
    sleep(0.5)
    dlp.write(b'QWERTYUI')  # sets all lines back to '0'

The following capture from a scope shows that, at the 115200 baudrate, the delay between the edges of the first and 8th line is less than 1msec.

Note: DLP design also manufactures modules with with 14 or 20 lines (see http://www.dlpdesign.com/usb/)

Here is the full list of commands:

ASCII	Hex	Description	Return
1	0x31	Ch1 Digital Out 1
Q	0x51	Ch1 Digital Out 0
A	0x41	Ch1 Digital In	0 or 1
Z	0x5A	Ch1 Analog In	voltage
9	0x39	Ch1 Temperature
2	0x32	Ch2 Digital Out 1
W	0x57	Ch2 Digital Out 0
S	0x53	Ch2 Digital In
X	0x58	Ch2 Analog In
0	0x30	Ch2 Temperature
3	0x33	Ch3 Digital Out 1
E	0x45	Ch3 Digital Out 0
D	0x44	Ch3 Digital In
C	0x43	Ch3 Analog In
-	0x2D	Ch3 Temperature
4	0x34	Ch4 Digital Out 1
R	0x52	Ch4 Digital Out 0
F	0x46	Ch4 Digital In
V	0x56	Ch4 Analog In
=	0x3D	Ch4 Temperature
5	0x35	Ch5 Digital Out 1
T	0x54	Ch5 Digital Out 0
G	0x47	Ch5 Digital In
B	0x42	Ch5 Analog In
O	0x4F	Ch5 Temperature
6	0x36	Ch6 Digital Out 1
Y	0x59	Ch6 Digital Out 0
H	0x48	Ch6 Digital In
N	0x4E	Ch6 Analog In
P	0x50	Ch6 Temperature
7	0x37	Ch7 Digital Out 1
U	0x55	Ch7 Digital Out 0
J	0x4A	Ch7 Digital In
M	0x4D	Ch7 Analog In
[	0x5B	Ch7 Temperature
8	0x38	Ch8 Digital Out 1
I	0x49	Ch8 Digital Out 0
K	0x4B	Ch8 Digital In
,	0x2C	Ch8 Analog In
]	0x5D	Ch8 Temperature
`	0x60	set ASCII mode
\	0x5C	set BINARY mode
L	0x4C	set °F
;	0x3B	set °C
'	0x27	Ping	Q (0x51) returned if DLP-IO8 is ok

A full description of the device is available at http://www.ftdichip.com/Support/Documents/DataSheets/DLP/dlp-io8-ds-v15.pdf

Installation

To use it under Python, you need to install pyserial:

 pip install pyserial

Under Linux, add yourself to the tty and dialup groups:

sudo usermod -a -G tty [yourlogin]
sudo usermod -a -G dialout [yourlogin]

Determine the serial port (Linux)

Once plugged, to determine the serial port the dlp-io8-g is attached to, type the command dmesg in a Terminal. You should get something like::

[ 5128.109725] usbcore: registered new interface driver usbserial_generic
[ 5128.109730] usbserial: USB Serial support registered for generic
[ 5128.112142] usbcore: registered new interface driver ftdi_sio
[ 5128.112148] usbserial: USB Serial support registered for FTDI USB Serial Device
[ 5128.112175] ftdi_sio 1-1:1.0: FTDI USB Serial Device converter detected
[ 5128.112190] usb 1-1: Detected FT232RL
[ 5128.113130] usb 1-1: FTDI USB Serial Device converter now attached to ttyUSB0

The last line tells you that the device is at /dev/ttyUSB0.

Examples

Writing on lines 1 to 8

from serial import Serial
dlp = Serial(port='/dev/ttyUSB0', baudrate=115200)  # open serial port

dlp.write(b'QWERTYUI')  # set all lines to '0'
dlp.write(b'12345678')  # set all lines to '1'

ON1 = b'1'
ON2 = b'2'
ON3 = b'3'
ON4 = b'4'
dlp.write(ON1 + ON2 + ON3 + ON4)

OFF1 = b'Q'
OFF2 = b'W'
OFF3 = b'E'
OFF4 = b'R'
dlp.write(OFF1 + OFF2 + OFF3 + OFF4)

Detecting changes on input line 1

   import time
   import serial

   dlp = serial.Serial(port='/dev/ttyUSB0', baudrate=115200)  # open serial port
   print(dlp.name)         # check which port was really used
   dlp.write(b'`')  # switch to ascii mode

   start = time.perf_counter()
   previous_state = '2'

   while True:
      dlp.write(b'A')  # request to read line 1
      state = dlp.read(3).decode('utf-8')
      if state[0] != previous_state[0]:
          print(time.perf_counter() - start, state[0])
          previous_state = state

Sending pulses at regular intervals

  #! /usr/bin/env python3

   """ Generate a square wave on pin1 of DLP-IO8-G """

   from time import perf_counter 
   from serial import Serial

   dlp = Serial(port='/dev/ttyUSB0', baudrate=115200)  # open serial port
   # byte codes to control line 1:
   ON1 = b'1'
   OFF1 = b'Q'

   # number of periods
   NPERIODS = 1000

   # Timing of the square wave
   TIME_HIGH = 0.010   # 10ms pulse
   TIME_LOW = 0.090    # send every 100ms
   PERIOD = TIME_HIGH + TIME_LOW

   onset_times = [ (PERIOD * i) for i in range(NPERIODS) ]

   i = 0
   while i < NPERIODS:
       if i == 0:
           t0 = perf_counter()

       # wait until the start of the next period
       while perf_counter() - t0 < onset_times[i]:
           None
           
       dlp.write(ON1)
       
       # busy wait for 'TIME_HIGH' seconds. This should be more accurate than time.sleep(TIME_HIGH)
       t1 = perf_counter()
       while perf_counter() - t1 < (TIME_HIGH):
           None
           
       dlp.write(OFF1)
       i = i + 1
       print(f"\r{i:4d}", end='')

   time.sleep(TIME_LOW)
   print()
   print(f'{NPERIODS} periods of {PERIOD} seconds')
   print('Total time-elapsed: ' + str(perf_counter() -t0))
   dlp.close()         # close the port

Here is the result on an oscilloscope:

chrplr/dlp-io8-g