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I am a beginner at electronics and I want to build a simple logic probe for TTL circuits. I found this diagram online:

schematic

Which does exactly what I want. However, I would like to make it play a high pitched sound when it is in high state and a low pitched sound when it detects a low state. I guess I would need some kind of speaker, but I don't know much about them, so basically I don't know where to begin or how to accomplish this, so any help will be appreciated.

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  • \$\begingroup\$ NE555 and LM358 would be a good place to start, for generating simple sounds. \$\endgroup\$ – MarkU Nov 12 '14 at 22:02
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You could add a piezo buzzer in series with your LED, put the high pitch one in series with the HEIGH LED and the a lower pitch in series with your LOW LED. They are quite cheap, small and work can work at low voltages so it would be perfect with to fit your circuit.

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Google "electronic buzzers" and choose one with high pitch and one with low pitch. Here is a page from Maplin that gives some ideas: -

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Here's a tri-tone one (on maplin page also): -

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There are plenty on the web and they work from DC so should easily interface to your circuit.

Here's a very small one that works from 1.5 volts to 5V: -

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