Serial port I/O module with 11 inputs — AVR

RS-232 input module, with 11 inputs. Rebuild of previous RS-485 module. Uses an AVR ATtiny2313 microcontroller.

Details

This I/O module is connected to the computer via the serial port. If the status on any of the 11 digital inputs changes; it will send a command string containing the module number, input number and new status. This also occurs on boot.

But — the module can not receive any commands, that makes it impossible to request an input status.

Noise and rebuild

This module was originally designed for RS-485 — but, as the image shows, the signals were drowned in noise. Later I found out that the cause of the noise was a lack of stabilizing capacitors. 10 µF and 1 nF was installed directly over the AVR and the problem was solved.

It was then rebuild into RS-232, which is a bit easier to interact with then the RS-485. The source code was rewritten to suit the RS-232, but I ran out of flash memory I had to remove input 12. Leaving the module with only 11 inputs.

I/O

Inputs

1. PB0 Input 1
2. PB1 Input 2
3. PB2 Input 3
4. PB3 Input 4
5. PB4 Input 5
6. PB5 Input 6
7. PB6 Input 7
8. PB7 Input 8
9. PD5 Input 9
10. PD6 Input 10
11. PA0 Input 11

Outputs

1. PD2 Life-signal
2. PD3 RS-485 Send enable (not in use)
3. PD4 Link activity LED

Interface

• PD0 RS-232 Rx
• PD1 RS-232 Tx

Connectors

15-pin

1. 5v
2. 0v
3. Input 1
4. Input 2
5. Input 3
6. Input 4
7. Input 5
8. Input 6
9. Input 7
10. Input 8
11. Input 9
12. Input 10
13. Input 11
14. Life-signal

9-pin

• 2 Transmit
• 3 Receive
• 5 GND

Communication

Interfacing is done with RS-232, using MAX232 or MAX202 and the SIOS protocol.

001:s:00:1:125 'boot
001:i:02:1:116 'input 2 on
001:i:01:1:115 'input 1 on
001:i:02:0:116 'input 2 off
001:i:01:0:115 'input 1 off
001:s:01:1:126 'life-signal

Serial settings

• Baud: 9600
• Data bits: 7
• Parity: None
• Stop bits: 1

Source code

Photos

Schematic drawing

Parts list

• 1 × AVR ATtiny2313-20PU, DIL-20, 20 MHz, 18 I/Os
• 5 × Capacitor, aluminium electrolytic, 1 µF, 50V
• 2 × Capacitor, aluminium electrolytic, 10 µF, 25V
• 1 × Capacitor, aluminium electrolytic, 47 µF, 25V
• 2 × Capacitor, ceramic, 1 nF, 100V
• 2 × Capacitor, metallized polyester foil, 10 nF, (0.01 µF)
• 1 × D-sub soldering cups, 15 pin male
• 1 × D-sub soldering cups, 9 pin female
• 1 × DIL socket, 16-pin, 7.62mm
• 1 × DIL socket, 20-pin, 7.62mm
• 1 × Enclosure, plastic (1591 FL), 120x65x40mm, flange
• 1 × Fuse 5x20 mm, 200 mA, fast-acting
• 1 × Fuse holder, open, PCB, 5x20mm
• 1 × Fuse holder, open, PCB, Protective cover
• 1 × LED 5mm clear, Yellow, 2.0V, 20mA, 250mcd, 6°
• 1 × LED 5mm coloured clear, Green, 2.1V, 20mA, 30mcd, 10°
• 2 × LED holder 5mm, RTC51, black plastic
• 2 × Mounting bracket, DIN rail, Plastic
• 32 cm2 PCB, stripboard, 100x160mm, 160cm2
• 13 × Resistor, carbon film, 0.25W, 330 Ω, 5%
• 2 × Resistor, carbon film, 0.25W, 4.7 kΩ, 5%
• 11 × Resistor, carbon film, 0.25W, 10 kΩ, 5%
• 1 × RS232 interface, MAX232CPE, dual
• 11 × Straight pin header, female, Single row, 2.54mm
• 14 × Straight pin header, male, Single row, 2.54mm
• 1 × Transistor, NPN, 100 mA, 45V, 0.5W, BC547B