A question about Experiment 11 in Make: Electronics (2nd edition)

Hi David,

I believe we saw a question on this experiment once before and if I recall there was a wire out of place. Can you attach / send a picture? Be sure to use the icons in the tool bar to insert links and pictures or they do not come through. Your link above does not work for me but I have the book so I could look it up. Do you have a multimeter? The authors schematic and breadboard layout are good so it should work. Test the speaker by putting a AA battery across the terminals briefly and listen for a click.

John

yes.  This has been posted before.  There was a wire out of place.  I reviewed this but cannot find my mistake.  I have tried multiple speakers.  I have tried different capacitors.  Here are the pages from the book:

I got this part working fine...

Hi David,

Do you have a way of posting a picture of your circuit so I can try to check it? If you can add pictures from several different angles as this helps sometimes. Did you have the LED flashing before you went to the speaker?

John

Make certain that the 1K resistor is connected between the emitter of the transistor and the ground rail as the circuit will not work otherwise.

I do have a 1K resistor connected on the emitter of the transistor and I did get the LED to turn on and off.  Here are some additional pictures.

Hi David,

Unless I am missing something your assembly looks good. What size capacitors are you using in the astable multivibrator circuit. Once possibility is that the oscillation is above the frequency range of the speaker. Have you tested the speaker by briefly putting a 1.5 volt battery across it to see if it clicks? You could go back to the LED set up to see if that is still working. If it is then install the speaker again without changing the capacitors. Instead of a flashing LED you should hear a click, click, click in the speaker. If you can get that working gradually decrease the size of the caps to hear the clicking increase in frequency. The best part of this exercise is that it is not working which will force you to solve the problem and in the course you will learn more than if it had worked the first time around. Keep up the good work, the fun is really in beating the challenge of things that don't work as expected. Also if you do solve the problem please get back to me as now I am interested,

John

I can get the light to blink reliably now.  I attach the LED with alligator clips and it works.  Then I attached the speaker to the alligator clips to speaker and it never chirps.  I can get the speakers to chirp if I connect them directly to the 1.5V or 9V battery.  But I never hear anything when I connect them to the circuit.

What does this mean?  Do I not have enough voltage across the speaker to drive it?  When I put 1.5V directly across the speaker I get a chirp. Or do I not have enough current flow?

If I attach my to the alligator clips to my multimeter it registers 8.2V.  Is this because it can't sense the voltage turning on and off?

l actually have an oscilloscope on the way.  Would I be able to measure the current and voltage on this circuit?

I am very puzzled I can't get this speaker to make any noise...

David

Hi David,

We are making progress. In the picture you are hooking the speaker in series with the 1K resistor. I am going to assume that the speaker has 8 ohms while it may have less. In this situation 99% of the power will be across the resistor and 1 % will be across the speaker. Hooked in this way there is probably not enough energy getting to the speaker to hear. Even hooked the way that it was described with the 100 uF cap in series with the speaker and parallel to the 1K resistance I do not expect it to be very loud. The LED does not have a resistance in the same way that the speaker does. It will demand a 1.2 volt drop across it when forward biased. The 1 K resistor along with the LED limits the current to approximately 7.8 volts divided by 1K or 7.8 mA. You should be able to figure out the things that you are asking about with the tools that you have and have coming but it will take some learning and experimenting. Even with the best tools a man isn't a carpenter until he practices and develops the skills. I think you are doing a great job. You should be able to use your meter to measure the DC resistance in ohms of the speaker. You should also be able to measure the voltage across the speaker, keep in mind with a capacitor in series with the speaker it will not be DC voltage but AC voltage. If you divide the AC RMS voltage by the resistance the formula will give you the current. Multiply the current by the voltage and you will have the watts being converted in the speaker. The oscilloscope will give you the added tool of being able to look at the shape of the signal as well as its magnitude. You will still have to do a little math to figure the current. Look at the speaker and see what the impedance is. the numbers are typically 4, 8, 16, or 40 ohms. The higher the resistance the better chance that you will be able to hear the sound.

John

Success!  I rebuilt the circuit again on a second breadboard and got it to work.  Then I went back to the original breadboard and found a bad transistor.  I have been making a lot of progress in learning about electronics -- fixed my first vintage receiver.  Thank you so much for your help and guidance.

David Brehm