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I am trying to get to get familiar with working with a 74LS148 Priority Encoder IC. I am providing a 5 Volt constant current voltage source to the IC and have a 0 Volt ground Voltage. I tried connecting every input to the 5 Volt source to set it on a HIGH logic state, which should give, according to the truth table, HIGH in the output. Then tried setting some inputs to LOW, but that had no effect in the output which remained in a HIGH state.

I then tried using pull up resistors, the use and circuit configuration of which is not entirely clear to me, which I think is the problem. I connected the resistors as shown in the picture below, which should give a HIGH state in the output. I then tried connecting some inputs, along with their resistors, to the Ground. The output still remained on a HIGH state, around 4.3 Volts.

I repeated the entire process with another 74LS148 IC to make sure the first one was working.

I'd could really use a little help. Thank you all!

enter image description here

74LS148 has the following truth table:

enter image description here

kwoxer
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Galux Trabakoulas
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    I’m voting to close this question because it's not a programming question. [electronics.se]? – DavidW May 07 '20 at 16:52

3 Answers3

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EI (pin-5) must low (connect to ground)

Kencit
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The enable E1 must be ground. you also your diagram indicates inputs 0 through 7 are pulled high. This will always produce your outputs to be HIGH

Phoenixcomm
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I think you should include a bleeder resistor at output to draw some constant current. This will help regulator function as desired.

gStam
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