- 5k1 resistor sets maximum current.
- 0.01 uF capacitor shunts RF spikes to ground.
- Zener diode clamps positive levels to 5.1 V and negative levels to -0.7 V.
- Single-point ground helps.
- 0.01 uF cap & 5k1 res. form a 100-kHz low-pass filter.
| You are in home \ microcontroller \ peripherals \ micro interface protection (back) |
|
- 5k1 resistor sets maximum current. - 0.01 uF capacitor shunts RF spikes to ground. - Zener diode clamps positive levels to 5.1 V and negative levels to -0.7 V. - Single-point ground helps. - 0.01 uF cap & 5k1 res. form a 100-kHz low-pass filter. |
 |
Transistor effectively isolates outside world from micro. Can be used in conjunction with above I/O protection cct. |
 |
This is a good driver for big/inductive loads, providing good protection. The BD139 has IC = 1.5 Amps. If only 500 mA is req'd, then replace entire cct. with ULN2802A 8-way darlington driver (DSE# Z-6282). |