Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Need help for 74LS08 one logic input with switch

Status
Not open for further replies.
P

PCBwire

Newbie level 6
Newbie level 6
Joined
Mar 27, 2010
Messages
12
Helped
0
Reputation
0
Reaction score
0
Trophy points
1,281
Visit site
Activity points
1,357
74LS08

74LS08 is simple AND.

I would like to control one logic input, with switch.

When switch is closed, both inputs are Vcc, and output is Vcc.

When switch is open, one input is open circuit, I would like for output to be Gnd, but i do not think it will be?

Mabybe to use switch which is changing form Vcc to Gnd, and not from Vcc to open circuit.
 

Re: 74LS08

By opening the switch you don’t change the stage of the input, it just goes from Vcc to floating (or undefined) potential that by the 08 gate is still read as “H” ..
With TTL gates you have to physically connected them to GND or use low-ohm pull-down resistor;
For TTL-LS gates (Iil<400uA, Vil<0.4V) the pull-down resistor can be 1kΩ ..

Rgds,
IanP
:|
 

    P

    PCBwire

    Points: 2
    Helpful Answer Positive Rating
Re: 74LS08

try something like this?
gate.jpg


EDIT: sorry cameo_2007. you hadn't posted when i clicked reply..
 

    P

    PCBwire

    Points: 2
    Helpful Answer Positive Rating
Nope, that second input is not always logic one, it is output of multiplexer so can be anything, and AND is needed. :)
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top