Serial port I/O module with 15 inputs — AVR

Serial (RS-232) interface module; providing 15 digital inputs. Uses an AVR ATmega8 microcontroller.

Details

This serial I/O module is connected to a computer serial port, and reports the status of 15 inputs. It is a rebuild of a previous module.

When an input is activated; the unit sends the status to the computer instantly. Each input has a hysteresis of three seconds to prevent unwanted rapid switching. It’s also possible to request the status of any input at any given time.

Every 20th second a life pulse is sent to Serial Server.

I/O

Inputs

1. PC0 In 1
2. PC1 In 2
3. PC2 In 3
4. PC3 In 4
5. PC4 In 5
6. PC5 In 6
7. PD3 In 7
8. PD4 In 8
9. PD5 In 9
10. PD6 In 10
11. PD7 In 11
12. PB2 In 12
13. PB3 In 13
14. PB4 In 14
15. PB5 In 15

Outputs

1. PB0 Life-signal (to Module stability monitoring unit 2)
2. PB1 Link activity LED

Interface

• PD0 RS-232 Rx
• PD1 RS-232 Tx

Connectors

Wires

• Red: 5V
• White: 0V
• Green: Life-signal

15-pin

1. In 1
2. In 2
3. In 3
4. In 4
5. In 5
6. In 6
7. In 7
8. In 8
9. In 9
10. In 10
11. In 11
12. In 12
13. In 13
14. In 14
15. In 15

9-pin

• 2 Transmit
• 3 Receive
• 5 GND

Communication

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

001:i:02:1:116 'in 2 on
001:i:01:1:115 'in 1 on
001:i:02:0:116 'in 2 off
001:i:01:0:115 'in 1 off
001:s:01:1:126 'life-signal

Serial settings

• Baud: 9600
• Data bits: 8
• Parity: None
• Stop bits: 1

Source code

Photos

Schematic drawing

Parts list

• 1 × AVR ATmega8-16PU, DIL-28, 16 MHz, 23 I/Os
• 5 × Capacitor, aluminium electrolytic, 1 µF, 50V
• 1 × Capacitor, aluminium electrolytic, 10 µF, 25V
• 1 × 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, 28-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
• 17 × Resistor, carbon film, 0.25W, 330 Ω, 5%
• 2 × Resistor, carbon film, 0.25W, 4.7 kΩ, 5%
• 15 × Resistor, carbon film, 0.25W, 10 kΩ, 5%
• 1 × RS232 interface, MAX232CPE, dual
• 22 × Straight pin header, female, Single row, 2.54mm
• 30 × Straight pin header, male, Single row, 2.54mm
• 1 × Transistor, NPN, 100 mA, 45V, 0.5W, BC547B