Interfacing question of different voltage levels

[Physicslearner500039]

Hi all,

i have this small interfacing problem somebody please suggest me how to resolve this problem. i have two hardware boards say unit 1 and unit 2. The Unit 1 has 48 digital inputs and outputs configurable through software as either input/ouptut but they are ttl level i.e 5V logic. i have unit 2 which is also having digital input and outputs but this unit needs 24V to detect as high (internal to unit2 24v is converted into 5V and given to microcontroller) and on its output it gives either 24V or 0V. Now i need to interface this unit1 and unit2

My clarifications are:

1. To connect digital output of unit1 of 5V by level shifting to 24V and giving it to unit2. please suggest some intermediate circuitry for this

as per my idea i think i can use 24v relays but it would be costly and using some 32 24V relayes would be difficult. could somebody some altenative and easy solutions.

2. to interface the unit1 digital inputs with unit2 digital outputs. since unit1 recongnizes ttl levels can i convert the 24v high from unit2 by using resistors and bring it to 5V and connect to unit1. Please provide some ideas for this.

what are the possibilities in which the unit1 5V I/O may get damaged or what care i have to take while interfacing with 24V system.

please let me know if you have further clarifications.

thanks in advance,

regards,
satya

 

[jim hardy]

if you're sure it's 24 volts not 30
check SN7407 datasheet.
http://www.cedmagic.com/tech-info/data/7407.pdf

does your unit 2 have internal pullup resistors on inputs?

 

[Physicslearner500039]

Thank you for the quick reply. i have drawn the internal diagrm of the Unit2 conversion from the 24V to 5V system and attched.

thanks and regards,
satya