About 74C922( Keypad encoder) - Electronic Circuits Projects Diagrams Free

kyutekyute101 · 26th April 2006, 12:43 PM

Hi
How come the data from the keypad encoder's output is lower voltage that its data sheet... ( when 5V Vcc is applied ). Do i need a pull up resistor to bring up the voltage ??? i REALLY cant find the solution for it....

Pls reply me.
Thanks

**Nigel Goodwin** · 26th April 2006, 01:04 PM

Quote:

Originally Posted by kyutekyute101

Hi
How come the data from the keypad encoder's output is lower voltage that its data sheet... ( when 5V Vcc is applied ). Do i need a pull up resistor to bring up the voltage ??? i REALLY cant find the solution for it....

How low is it?, and how are you measuring it?.

G8RPI · 28th April 2006, 02:44 PM

Hi,
The 74c922 is compatable with both CMOS and low power TTL. The output voltage "high" when connected to CMOS (assuming 5V supply) is specified as 4.5V minimum. However when connected to TTL, it is only specified as 2.4V minimum. If you are connected to TTL and the high voltage is above 2.4V the IC is within specification.
The only other possible problem is that you are not pulling the output enable input (pin 13) low and noise is causing a PWM like modulation of the output. This problem would be obvious with a 'scope but not a voltmeter.

G8RPI.

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26th April 2006, 12:43 PM	(permalink)
kyutekyute101	About 74C922( Keypad encoder) Hi How come the data from the keypad encoder's output is lower voltage that its data sheet... ( when 5V Vcc is applied ). Do i need a pull up resistor to bring up the voltage ??? i REALLY cant find the solution for it.... Pls reply me. Thanks __________________ Nothing special.

28th April 2006, 02:44 PM	(permalink)
G8RPI	Hi, The 74c922 is compatable with both CMOS and low power TTL. The output voltage "high" when connected to CMOS (assuming 5V supply) is specified as 4.5V minimum. However when connected to TTL, it is only specified as 2.4V minimum. If you are connected to TTL and the high voltage is above 2.4V the IC is within specification. The only other possible problem is that you are not pulling the output enable input (pin 13) low and noise is causing a PWM like modulation of the output. This problem would be obvious with a 'scope but not a voltmeter. G8RPI.