Electric heater and timer controller — AVR

Controls an electric heater, and has a simple 15 minutes timer. Uses an AVR AT90S2313 microcontroller.

Details

• The module turns off the heat in the living room when the porch door has been open for 20 seconds. 90 seconds after the door has been closed; the heat is turned back on. The heat can also be disabled using an external switch.
• A short signal pulse from another module or a switch, will activate the output for 15 minutes. Used for turning on the test voltage on the Rack status panel. A new pulse within these 15 minutes turns the output off.

Leakage current

The solid state relay used for the heater, leaks a small amount of current, about 10mA. This can be eliminated using a resistor in parallel over the oven supply after the relay. A 22K, 5W resistor should be the job.

I/O

Inputs

1. Porch door, from Multi-purpose module 1
2. Manual oven disengage
3. Signal activate

Outputs

1. Oven relay N.O
2. Oven relay N.C
3. Oven LED
4. Oven local LED
5. Signal output
6. Life-signal (to Module stability monitoring unit 2)

D-Sub 9-Pin

• Red: 5v
• Black: 0v

1. Input: Porch door
2. Input: Manual oven disengage
3. Input: Signal activate
4. Output: Oven relay N.O
5. Output: Oven relay N.C
6. Output: Oven LED
7. Output: Signal
8. Output: Life-signal

Source code

Photos

Schematic drawing

Parts list

• 1 × AVR AT90S2313-10PI, DIL-20, 10 MHz, 15 I/Os
• 1 × Capacitor, aluminium electrolytic, 10 µF, 25V
• 2 × Capacitor, ceramic, 22 pF, 100V
• 1 × Capacitor, ceramic, 1 nF, 100V
• 1 × D-sub soldering cups, 9 pin male
• 1 × DIL socket, 20-pin, 7.62mm
• 3 × Diode, small signal, 1N4148/Ph
• 1 × Enclosure, plastic (1591), 100x50x25mm
• 1 × LED 5mm coloured clear, Green, 2.1V, 20mA, 30mcd, 10°
• 1 × LED 5mm coloured clear, Red, 2.1V, 20mA, 8mcd, 10°
• 2 × LED holder 5mm, RTC51, black plastic
• 2 × Mounting bracket, DIN rail, Plastic
• 1 × Quartz crystal oscillator, 4 MHz
• 5 × Resistor, carbon film, 0.25W, 330 Ω, 5%
• 6 × Resistor, carbon film, 0.25W, 4.7 kΩ, 5%
• 3 × Resistor, carbon film, 0.25W, 10 kΩ, 5%
• 1 × Switch, toggle, 1-pole, micro, on-on
• 5 × Transistor, NPN, 100 mA, 45V, 0.5W, BC547B