Is this good practice to use an NPN transistor as an active low switch like this please read description

218

01:24:09

I'm still a rookie with transistors and have never seen this done before so I'd like to know if this is okay to do or bad practice. The logical 1 switch represents a micro controller and the JK flip flop represents a sound module. The sound module is activated only when pin "J" is shorted to ground. I found this in a schematic for this module I'm currently using. Even though it works, I would like to know if this is the proper. If so, shouldn't there at least be a pull up resistor between the collector and pin "J"?

published 8 years ago

hurz

8 years ago

You have to define the voltage level in case the transistor is not active. This is called pullup resistor. http://everycircuit.com/circuit/6090408827551744

Link16

8 years ago

I see Thanks @hurz Yeah that makes sense. So to summarize... The circuit design is incorrect/improper since pin "J" is floating when the transistor is not active. The correct way is to attach a pullup resistor to the node between the collector and pin "J" so there is a defined voltage level (it's no longer floating). Is that correct?

hurz

8 years ago

EveryCircuit logic gates are CMOS onces, and floating input at CMOS gates is even dangerous for the IC. In case of TTL, open input are allowed and logical HIGH, even its for performance not done. But for standard TTL, an extra pullup is not needed.

lenzrulz

8 years ago

Just a different idea: http://everycircuit.com/circuit/4527672628871168

raichea

8 years ago

A pullup is required. Check the chip spec to see if an internal pullup is provided at pin J. If not, an external one is needed.

hurz

8 years ago

@Link16, can you make a picture of input config J schematic, so I can check that. BTW, are there any IC connected close to and which one. Anyway, if you have a specification of this "sound module" there is propably more in detail.

hurz

8 years ago

So many tipps, inclusive troll propaganda, and now @link16?

Robert_Kidd

8 years ago

@hurts, stop trolling. Just concentrate on the electronics. You are paranoid.

hurz

8 years ago

Amused

LuenOrga

8 years ago

It should! You need a pull up resistor. Pins JK work as inputs so you need an external power supply and resistor. Pin J is connected between collector and pull up resistor

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