Pull-down

Aug 01, 2006 3 Replies
J

Hello,



I sincerely apologise for the phenomenally newbie question but here goes....


I have an ISD1730 chip which essentially plays a sound thru a speaker whenever one of the pins drops low, it has an internal pull up resistor. How can I use a non-physical switch to trip it? Basically I would like to have an Astable circuit trip it. How can I do this? Can I just put the output of an Astable onto it; or would I have to put a NOT gate in between so it is always high then goes low on the high pulse from the astable???



Please help


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D

one of the pins drops low, it has an internal pull up resistor.

have an Astable circuit trip it. How can I do this? Can I just put the output of an Astable onto it; or would I have to put a NOT gate in between so it is always high then goes low on the high pulse from the astable???

Need a little more information.

If your npot using a "switch", what are you using ??

An opto-isolator would work if I know what was controlling the opto.

Help me, help you !

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J

You could use an astable with complementary outputs and drive the 1730 with the negative-true output, or if you wanted to use something like a 555/7555 you could do this: (View in Courier) IDS 1730 +----+ |_ | +---O|E | | | | C +----+ ASTABLE OUT>---[1KR]---B 2N3904 E | GND
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