Input circuit to microcontroller

[juhhi]

Hello!

I have spent last couple of days using Multisim and Google and trying to design input circuit to microcontroller (AVR) with following requirements:

1. Incoming signals: TTL-level pulse sensor, open-collector Hall-sensor and automotive switch-type input (+13,6V - open circuit)

2. Frequency range would be from discrete input (0,1Hz I quess) to 10kHz

3. Environment is a car so the input should be capable to protect controller against transients

I have facilities to use SMD components. Following component are available for use (and the cost I not the first thing to worry about, so missing components can be ordered):

Optocoupler IL205AT
Diode network BAV199
Zener diodes 4,7 to 9,1V (BZX84...)
NPN and PNP transistors BC807, BC847
Schmitt-triggers
etc.

Basically these input signals are easy to handle, but when trying to achieve all off them with only one type off circuitry the problems begin...
Any ideas are most welcome!

 

[IanP]

Try to differentiate between signals comming from highly hazardous sections (ignition, for example) and those comming from low-voltage sensors ..
In the former option good protection and signal conditioning can be provided by resistor-zener diode-optocoupler combination ( see example at: ), in the latter one you can consider simple resistor-diode(to Vcc)-diode(to Vss) input protection before feeding signal directly to microcontroller ..
Obviously, a good supply voltage filtering, or even dc-dc isolation, in this environment is a MUST ..

Regards,
IanP