SawTable
An ATmega32u4 based thingy for driving liniear actuators for table legs and controlling a dust collection system in my table saw table
Current transformer
The current transformer outputs 1000:1 current, so 5 A through the primary gives a 5 mA secondary current.
I want the maximum current to be 8 A on the primary, so that's 8 mA on the secondary, which I want to measure with an ADC input on the AVR running at 5V, so full ADC range is 0-5 V.
To detect the averaged current easily I'll use a diode detector with a 10uF + 100k discharge resistor.
The diode drops 0.7 V, so I need full range (8 mA) to result in 5.7 V at the transformer, so the ADC sees 5V.
A resistor that drops 5.7V at 8 mA is 712 Ohm, rounding off to the nearest E24 value gives me 680 Ohm and a full-range of 0 - 8.4 A.
Pin assignments
| Define | AVR | Pin | Description |
|---|---|---|---|
| VALVE_A | PD3 | 1 | Internal pullup, pulled low when valve is in position A |
| VALVE_B | PD2 | 2 | Internal pullup, pulled low when valve is in position B |
| LEG_A_DOWN | PD1 | 5 | H-Bridge for leg A, down |
| LEG_A_UP | PD0 | 6 | H-Bridge for leg A, up |
| LEG_B_DOWN | PD4 | 7 | H-Bridge for leg B, down |
| LEG_B_UP | PD6 | 8 | H-Bridge for leg B, up |
| PD7 | 9 | ||
| PE6 | 10 | ||
| LEG_A_SENSE | PB4 | 11 | Internal pullup, pulled low by pulse sensor in leg A |
| LEG_B_SENSE | PB5 | 12 | Internal pullup, pulled low by pulse sensor in leg B |
| BUTTON_3 | PB6 | 13 | |
| BUTTON_2 | PB2 | 14 | |
| BUTTON_1 | PB3 | 15 | |
| BUTTON_0 | PB1 | 16 | |
| VALVE_MOTOR | PF7 | 17 | High runs valve motor |
| VAC_MOTOR | PF6 | 18 | High runs vacuum motor |
| CURRENT_B | PF5 | 19 | ADC 5 current sense input for equipment B |
| CURRENT_A | PF4 | 20 | ADC 4 current sense input for equipment A |
Control scheme
- Up/Down Both legs up/down at full speed.
- 1: Leg A up, Leg B down.
- 2: Leg A down, Leg B up.
- 3: Toggle park / deploy.
- S: Toggle manual vacuum on external port.