Additional Information

[nabhatti]

for the extended circuit, can i use 2N3904 NPN transistor instead of BC337 and 2N3906 PNP transistor instead of BC327
thank you

[audioguru]

Hi Naveed,
Sure you can use your replacement transistors. The current is only 10 mA and they won't have more than about 6V across them if you use a 9V battery.

The project clearly says to use a single Q1 and Q2 circuit, and series connected LEDs (I don't think more than 2 or 3 in series with a 9V battery) connected in strips. The lower LED of each strip is driven by a separate Q3/R9 circuit from the outputs of IC2.

[nabhatti]

if you look at the extended circuit, there is a R9 terminal and a terminal at the top with a (+) sign beside it. where will we connect those terminal in the original circuit.

[audioguru]

Like this:

[nabhatti]

the terminal labeled (+) beside R11 will be connected to the battery right.
im talking about the extension circuit.

[audioguru]

Yes, (+) on the extension circuit connects to the positive supply.

[nabhatti]

in the project fading LED's under motor, light and power control, R5 is it a 2 Mohm resistor or 22 Mohm. also R1 and R2 are 47 K right.
The values of C1 and C2 , are they nano farod or micro farad.
the units are not clearly shown.
that is why i am asking you
thank you

[audioguru]

Hi Naveed,
You can't read the way Europeans write component values? They use the multiplier letter instead of the decimal point.
R1 and R2 are 4.7K
R5 is a 2.2M trimpot
R12 and R16 are 56 ohms.

The author's new website shows C1 as 1uF and C2 as 100uF.

[nabhatti]

Hello audioguru,

I am naveed's team partner. Thank you for helping us with
the dancing LEDS.

We are at a point where, we really need to get some
specific information related to this circuit(Dancing LEDS).
Some thoughts i had for the specification are:


1)what can we predict about the capacitors in this

circuit.Like how much time will it take to charge up and

how long to discharge during the circuit operation.

2)what will be the error percentage for the amplifing

factor

3)what can we tell about the signal characteristic after it

passes through the first opamp, capacitor, second op-amp,

diode,right before the clock input and at the counter

output respectivly compared to the input signal.
For example:what percentage will be the amplitude of the

signal right before it enters the counter, compare to the

input of the circuit.

the above details i am hoping to use as the specification

for the circuit. I will appreciate if you can help us with

the above specification or if you can give some other

specification for this circuit with better behaviors, that

we can test out.

one more question: i was curious why we have that capacitor

c5 in  parallel to the battery B1.

thanks once again!!!

[audioguru]

Hi Naveed's team leader,
You don't need to write a specification for the simple circuit of the Dancing LEDs project. Its operation depends entirely on the amount of sound level picked-up by its microphone. The sound level is determined by its power, closeness to the microphone and room acoustics.

1) Only C4 is charged by the recifying action of IC1B and D1. The charging current isn't limited by a resistor so is as fast as the small amount of output current from IC1B will allow. The output current of the opamp is spec'd from a minimum of 20mA, a typical of 40ma and no maximum but probably no more than about 50ma. The low-power opamp has a very slow slew-rate that also might limit the charge quickness of C4.
The charging speed of C4 doesn't matter anyway since the 4017 counter has a Schmitt-trigger action on its clock input, so it will trigger properly on any slow speed of input signal.
C4 is discharged only by R7, therefore the discharge time is 330n X 100K = 33ms.

2) The amplifying error of IC1A id determined by the accuracy of R4 and R5 since the opamp has an open-loop gain of about 30,000 at 30Hz. Its gain should be 1+(100K divided by 1K) = 101. IC1B has 100% negative feedback so its gain is exactly 1 for positive half-cycles of the output of !C1A.

3) IC1A amplifies frequencies above the high-pass filter action of the mic impedance in parallel with R1, R2 in parallel with R3, and C1. The amplification of low frequencies is also reduced by the high-pass-filter action of R4 and C2. The high frequency amplification of IC1A is limited by its low bandwidth and low slew rate and will drop above about 5KHz.
Since IC1A and IC!b have a combined gain of 101, the amplitude of the signal entering the counter is 101 times larger than the input, depending on frequency and tolerance of R4 and R5.

C5 is used to smooth the output voltage of the battery which will fluctuate wildly when the battery runs-down and its internal resistance increases. The recifier pulses of up to 50mA cause the wild voltage fluctuations without C5.

Did Naveed get the project working? He had a problem with its microphone. If he replaced the microphone, how does the project respond to music? Can you place its microphone far enough away from a speaker so that the LEDs step along in time to the music's beat? If the microphone is too close to a speaker are the LEDs a dim blur?  Do the LEDs step along with each spoken syllable? ;D   

[nabhatti]

thank you very much sir
i did made the project work and its doing whatever its supposed to do , moving the LED's along with the music.
just one question . for the extended circuit, we have transistors that make up a 10 mA current source. how is that 10mA helping us in lighting the strips.
once again i thank you from myside and from my team members for helping us.
thank you

[audioguru]

Hi Naveed and team,
Good, it works. I am glad to have helped you.  ;D

Q1 and Q2 keep the current constant at 10mA with only 1 LED or two or three. They also keep the current constant when the battery runs down. Q3 saturates well so that most of the supply voltage is available for the LEDs.

[nabhatti]

could you please explain why do we need C2 in series with resistor R4?
how is that capacitor effecting the rest of the circuit?
by increasing the value of C4 , will we increase the circuit speed or decrease it

[audioguru]

Hi Nab,
For the Dancing LEDs project, if you remove C2 then IC1A will be a follower with a gain of 1 instead of the desired gain of 101. If you bypass C2 so that R4 connects to ground, the output voltage of IC1A will be saturated against the positive supply. An opamp with negative feedback will do with its output whatever it can to keep the voltage of its inputs the same. With R4 grounded, the opamp is trying to force its output voltage to +455V!
At DC, C2 disconnects R4 from ground so that the opamp is a voltage follower with a gain of 1. Using a 9V supply, its inputs and output voltage will be 4.5V. But for AC signals above about 16Hz, the capacitive reactance of C2 is low and the opamp has a gain of 101.

If you increase the value of C4, it will take a little longer to charge by IC1B so there might be a noticeable delay from a loud sound happening and the 4017 stepping to the next LED. Also, an increased value of C4 will take longer for it to discharge into R7 so the 4017 won't be able to step as quickly as before. ;D