# Please check the connections of this circuit

Discussion in 'General Electronics Chat' started by dumindu89, Jun 28, 2012.

1. ### dumindu89 Thread Starter Member

Oct 28, 2010
113
0
Please tell me that the DIP switches connected are connected with the correct way or not.
I need to give "1" or "0" to each ABCD inputs (as I need) of the each counter using DIP switches.
If they are not connected correctly tell me how the should be connected.(specially Vcc and GND of DIP switches).

2. ### BSomer Member

Dec 28, 2011
433
106
I think that you need to put in some pull up/down resistors on the inputs. They way you have it, when the switches are on the inputs are "floating". Generally what is done is the inputs are tied to VCC through a 10k ohm resistor. The inputs also connect to ground through the switch. So when the switch is off the input is pulled high through the resistor, when the switch is on the input is pulled low to ground.

3. ### KMoffett AAC Fanatic!

Dec 19, 2007
2,584
234
74XXX TTL's inputs are "normally" high. You need a pull-down switch or resistor the force a low input. As BSomer said, a pull-up resistor is desirable if the input is left floating.

Two switching methods (from TTL Cookbook):
1. 2.2KΩ between input and +Vcc, and switch between input and ground. Switch closed = low
or
2. 330Ω between input and ground, and switch between input and +Vcc. Switch closed = high

Ken

dumindu89 likes this.
4. ### dumindu89 Thread Starter Member

Oct 28, 2010
113
0
Hi!
I would like to go with the second method; switch closed = high which is the common one.

Do you mean the circuit should be as follows (assume resistors are 330 ohms)?

Last edited: Jun 29, 2012

Dec 19, 2007
2,584
234
Looks right.

Ken