µC ADC

by Martin Clausen (mc AT rotgradpsi DOT de)

This circuit employs a MCU to digitalize the photo current of up to eight photodiodes or any other current or voltage sources with 16 bit resolution.

• Features
• Usage of Device
• Parts
• Download of Program and Circuit

Features

• up to eight inputs with 16 bit resolution
• integration times from 100µs to 1s and 6.5s
• 8 general purpose in-/output lines
• up to 255 devices cascadeable
• all commands from the computer pass through with a delay of only 29µs plus send time of one character, while no measurement is done
• 128 bytes communication buffer
• RS232 interface, 8 databits, no parity, one stopbit
• supported baudrates: 115.2; 57.6; 38.4; 19.2; 9.6; 4.8; 2.4 and 1.2 kbps
• line end character: CR; other possible, please send me a mail
• LED shows activity
• low part count
• Program is freeware for non-commercial use.

Usage of Device

The line end character can be changed easily, just send me a mail with your demands.

The LED will be on after power-up. After each correct command it will toggle between on and off. If a buffer overflow occurs, the LED will stay permanently off and the MCU is stopped.

The measurement is done when a falling edge appears on the interrupt pin. If you want to control this pin via RS232 you could use a GPIO pin. There is no direct control of this feature via software.

The GPIO is written via the lower byte of command 3, all other bytes are dummies. Reading is possible via command 4. Here all bytes send are dummies. The state of the GPIO after reset is high.
Note that you need to write an one to a GPIO before it is possible to use it as an input, if it has been used as an output since the last reset.
The GPIO lines are located at P2 of the MCU. They are open collector outputs with a weak pull-up resistor and contain also a circuit for read back. Refer to the microcontroller datasheet for details.

Messages from the controller are sent with its own address first and then followed by the data in hex-code (nibble by nibble from msb to lsb).

Baudrate Selection

Meaning of 1 and 0 in this table:

Sign	Switch
1	closed
0	open

The baudrate jumper are read up on reset.

Parts

• Semiconductors:
• 1 AT89C52 or AT89S52, 24MHz; see also programming tips
• 1 MAX232
• 1 78L05
• 1 ADS8344
• 1 MC1403
• 1 low current LED
• for eight current or photodiode inputs:
  • 1 78L05
  • 1 79L15
  • 8 IVC102

  Capacitors:

• 1 1µF / 6V
• 2 4.7µF / 6V
• 8 10µF / 25V
• 2 33pF cer
• 2 10nF cer
• 6 100nF cer
• for eight current or photodiode inputs:
  • 4 10µF / 25V
  • 20 100nF cer

  Resistors:

• 2 10k*4 array
• 2 10
• 1 1k

  Mechanic:

• 1 22.118MHz crystal
• 2 sub-D socket, 9 pin
• 1 case
• 1 pbc
• 1 some thin wire
• 1 loop back plug (9 pin plug with only pin 2 and 3 connected to each other) for the last controller in a chain only

Download of Program and Circuit

• ucadccom.html communication protocol documentation
• Please contact me for details. (mc AT rotgradpsi DOT de)