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- EDA Theory
- Elementary Electronic Questions
- Thread starterroomy
- Start dateMar 22, 2011
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- Mar 22, 2011
- #1
R
roomy
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hello every one ,
i need helpe for making reset inmy circuit coz i try in pin 2and 3 on 47ls90 but doesnt work any suggest , please find attached above View attachment Doc23.rar
- Mar 22, 2011
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K
Kral
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To blank the display, connect pin 4 (Bl/RBO) to logic zero (ground). This will blank the display regardless of the state of the other inputs.
.
To Reset the counter to 0000, connect both Pins 2 and 3 to logic one.
- Mar 23, 2011
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R
roomy
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Hi,
can you tell me where can i put a switch and how many switch i need
thanks
- Mar 23, 2011
- #4
K
Kral
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To provide a counter reset function:
Remove the connections from R01 (Pin 2), R01(Pin 3) to ground.
Connect Pins 2, 3 Together.
Connect a "pullup" resistor from pins 2,3 to Vcc. The value is not critical. 47K will do.
Connect a SPST switch (or pushbutton) between pins2,3 and ground.
The "Reset" state is when the switch is open.
.
To blank the display:
Remove the connection between Bl//RB0 (Pin 4) and Vcc
Connect a "pullup" resistor between pin 4 and Vcc.
Connect a SPST switch between pin 4 and ground.
When the switch is open, the decoder works normally.
When the switch is closed, the decoder will blank the display.
- Mar 23, 2011
- #5
R
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hi,
thank you so much it works and any comment for my circuit i attached tell me
i have one qestion about the truth table for 74ls90
which is when R0(1) and R0(2) high doesnt count and the out put low but in my circuit when they high count . can you explain me this point coz amconfused about it , thanks
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- Mar 23, 2011
- #6
K
Kral
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I am also confused. The data sheet truth table clearly shows that when R0(1) and R0(2) are both high, the outputs are low, If either Rg1 or Rg2 is low. Did you measure the input voltage on Pin2,3 to check that the voltage is = to Vcc when the switch is open?
- Mar 23, 2011
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R
roomy
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can you tell me how i can measure the voltage on pin 2and 3
- Mar 23, 2011
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- Mar 24, 2011
- #9
K
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The circuit is correct. To measure the voltage on pins 2,3, just connect a voltmeter or oscilloscope beteen pin 2 or 3 and ground.
- Mar 24, 2011
- #10
R
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thank you for help
on the other day i submitted my circuit to my teacher without switches and he said what the specification for the circuit ,
but i said i have chosen resistors and capacitors and he said this is technical specification
do you have any specification for the circuit
can you write your email,i would like to send to you my report for this circuit to check if the report is poor or sufficient , if you don't mind
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