Need help with a scheme

[Drogarush]

Hello,

I'm a Norwegian student who currently is studying for an upcoming exam in electronics, and as a preparation, I've gotten this scheme I am having trouble with. I've figured out 2/3 of the schemes, but I just can't get this one right. Any help would be appreciated.

 

[Nigel Goodwin]

What can't you figure out?, it's just a way to destroy an LS244 by trying to use it as an H-Bridge.

 

[Drogarush]

What can't you figure out?, it's just a way to destroy an LS244 by trying to use it as an H-Bridge.

It's the LS244 I can't figure out how works.

 

[Papabravo]

All the information you need is in the symbol. It is a buffer, the output equals the input. Check the datasheet for the drive characteristics. I think it can sink more current than it can source. The outputs are three state outputs, they can be low, or they can be high, or they can be high impedance. The enable signal goes to the box on top with small indentations. The whole idea behind the construction of those symbols was to make the function unambiguous. I guess they forgot to give the secret decoder ring.

I'm with Nigel on the potential for destruction of the part.

 

[Drogarush]

Ahh okay, thanks for the help. It is greatly appreciated.

 

[audioguru]

If you have an extremely weak little motor then the circuit might drive it.
The minimum source current of each buffer is 15mA and the voltage might be as low as 2V. Look in the datasheet.

So if the motor runs with 1.8V at 30mA then it is fine.

 

[HarveyH42]

They use these type of circuits for B.E.A.M robots. Usually it's a 74HC240, and they stack 2 or more in parallel (yes, stack. one on top the other). The motors are tiny, often cellphone vibrator motors.