Become a subscriber (Free)

Join 29,000 other subscribers to receive subscriber sale discounts and other free resources.
Don't worry -- youre-mail address is totally secure. I promise to use it only to send you MicroZine.

Listening to Digital Signals

The buzz option on a multimeter is really useful because it tells you immediately when there is a short, without you having to read the resistance reading on the display.

The following circuits use a similar idea except that they don't check for shorts, but let you listen to digital signals in your circuit.

The main use for this circuit I have at the moment is to listen to the ICSP signal from MPLAB X when programming a chip. MPLAB X can take quite a while before it has re-built the code (C) and then started the programmer (software) and then gets around to do the actual programming (a different piece of software). All the while you are left staring at the screen waiting for the "programming complete" message to appear!

Then you can test the code out - probably finding that you left out a tiny action and therefore have to go through the whole process again!

This listener circuit lets you forget about MPLAB X so you can do another task such as examining the code you are writing or reading the datasheet etc. Since you can listen for the end of programming using this circuit it means you can save some time which is always a good thing.

Figure 1 shows use of a digital logic FET that has, as you would expect, a gate voltage that is sensitive to logic levels. For the 2N7000 Vgs is between 0.8V and 3.0V - if you need 3v3 logic the 2N7002 has Vgs from 1V to 2.5V but for typical values the typical Vgs for both parts is 2.1V

The 2N7000 is very useful as it does not draw current through the gate so it can be attached to any (logic) signal in your system. This is in contrast to the circuit shown in Figure 2 where a darlington pair is used - in this case a small current is drawn through the base via the 1k resistor

digital listener circuit 2N7000

The darlington pair (Figure 2) stops too much current being drawn through the base (as is the case when a single transistor is used) since the Beta (current gain) of each transistor multiplies the other. It is similar in operation to the FET except that its trigger voltage is ~1.4V.

digital listener circuit darlington

If you want to listen to different signals (perhaps they occur at different times) e.g. ISCP and serial output then Figure 3 shows how to use two diodes as a diode-OR gate.

digital listener circuit diode-or-gate

Note: you can use a piezo crystal (mine was attached to the case of an old watch which meant it should be louder - but it was still too quiet!)

Note: you can use any old NPN transistor eg, with Beta 100 or better.

New! Comments

Have your say about what you just read! Leave me a comment in the box below.

Privacy Policy | Contact | About Me

Site Map | Terms of Use

Visit our Facebook Page:

   Click Here

Recent Articles

  1. PIC PWM: Easy Pulse width Modulation on the PIC Micro.

    PIC PWM : What its for and how to use it. Including an example showing typical setup of a PIC PWM module with register settings.

    Read more

  2. The Essential I2C Tutorial: All you need to know about I2C...

    How to use I2C. In this tutorial you will learn all about the 2 wire I2C serial protocol. Learn how easy it is to use, how it works and when to use it...

    Read more

  3. PIC LCD volt meter : How to use the ADC for voltage measurement.

    A 0-5V LCD volt meter project using an HD44870 display and one PIC micro ADC.

    Read more

  4. PIC Programming using ICSP

    PIC programming : How to use ICSP for programming a PIC microcontroller giving some ICSP connection diagrams and it also shows how to use MPLAB X and ICPROG.

    Read more

  5. PIC ICSP In Circuit Serial Programming

    How to program PIC ICSP, IN-Circuit, live and still have a working programmer and operational circuit!

    Read more

  6. An Ultrasonic Distance meter project: How to make one using a microcontroller.

    Understand how an Ultrasonic Distance meter works by building one your self – including Free software to drive the microcontroller and display.

    Read more

Sign up for MicroZine
''The'' Microcontroller Newsletter

Enter your first Name and primary email address in the form below:

And receive absolutely FREE a full project for:

"Measuring Analogue Voltages
Without An ADC"

(Using only one pin).

Instant Download:
You Can
Get It Right Now

Warning: This project could be  Removed 
at any time.  

It will  NOT be 
available indefinitely SO
To avoid 
disappointment  get it:


Don't worry -- your e-mail address is totally secure. I promise to use it only to send you MicroZine
Remember this is a project with full description and fully debugged C Source code - and it's not available from the main website.

You can only get it through this newsletter.

To get exclusive access Enter your first name Name and primary email address Now in the form above.:

But wait !

There's more...

You'll receive more
free and exclusive reports as well as site information and site product updates

Scroll up to the form above and sign up NOW. Don't forget it's FREE and if you don't like it, you can unsubscribe at any time.

Click Here Now to use the form above to get your Valuable information absolutely free.

Readers Comments

"I wanted to thank
you so so so much
for all the information
you have provided in
your site it's


- Ranish Pottath

"This site really is
the best and my favorite.
I find here many useful
projects and tips."

- Milan


"Awesome site,
very, very easy and nice
to navigate!"

- Matt

Learn Microcontrollers

"Interested in

Sign up for The
Free 7 day guide:


"I am a newbie to PIC
and I wanted to say
 how great your
site has been for me."

- Dave


"Your site is a great
and perfect work.

- Suresh


"I couldn't find the correct
words to define
yourweb site.

Very useful, uncovered,
honest and clear.

Thanks so much for
your time and works.

- Anon

Back to Top