EXPERIMENTAL
Design of a sound to light effects Circuit.
DESIGN:
First experiment and gather data considering the biasing of the mosfet.
" * " = arbitrarily chosen value.
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*VCC = 8v.
*VGQ1 min. = 2v.
*VGQ1 max. = 6v.
*VSQ1 off = 1v.
VDQ1 off = 8v.
*VDQ1 on = 6v.
*RDQ1 = 68 ohms
IRDQ1 on = calculates to be 30 mA.
RS1Q1 off... calc.to be 33 ohms.
RS2Q1 off... calc. to be 220 ohms.
*RG1Q1 = 470 ohms
RG2Q1 calc. to be 160 ohms.
*RL1 = 100 ohms.
Now some thing to consider is that when Q1 is conducting RDQ1 causes a heavy positive voltage due to the small resistance across Q1 so VSQ1 rises from 2v. to around 3v. because of the parrallel resistance between RS2Q1 and RDQ1. But since VGQ1 is at 6v. the mosfet is able to continue conducting properly.
This is breadboarded and it measures out to around 6v. at the gate, VGQ1.
Mosfet stage
--------------------------------
Now that is the voltage needed to turn the output ON. (LED ON)
Now to turn off the output (LED OFF) the VGQ1 needs to be around 2v.
Calculations are as follows.
With 2v. VGQ1 then 6v. is dropped across RG2Q1, which makes a total current of 37.5mA.
Now 2v. will drop across RG1Q1 which gives a current of 4,25mA. Therefor the remainder current will flow through Q2 which is 33.25mA. (IEQ2)
*VBQ2 = 1.5v.
VEQ2 = 0.8v.
So REQ2 calc. to be 24 ohms.
*RB1Q2 = 240 ohms ( 10 times REQ2.)
RB2Q2 calc. to be 1K ohms.
Q2 stage
-------------------
Now with the VBQ2 established at 1.5v. then the VCQ3 is 1.5v. so make VBQ3 lower for proper biasing at around 1v. That makes VEQ3 around 0.3v.
REQ3 calc. to be (VEQ3 / IEQ2) = 9.1 ohms.
Now split the REQ2 into 2 resistors with a 9.1 ohms going to Q3's emitter, and (24 - 9.1) = ~15 ohms to go to Q2's emitter.
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Q3 stage
----------------
INPUT STAGE
--------------------------------
Now I need to implement a PNP transistor for the inputs of the next stages, because the signal output is a negative going signal.
*RCQ4 = 1K ohms, this is to tie the base of Q3 to ground so it's not floating and keeping any eratic RF noises away from base of Q3.
*VBQ3 on = 2v.
So IRCQ4 on = 2mA.
and I'll make around 2.5v. dropped across Q4 .....*VCEQ4.
REQ4 calc. to be around 2.7K ohms.
Now that is the configuration of the succeeding stages after the first input stage.
Now I breadboarded the input stage plus 3 more of the above stages taking the output of each stage into the base input of the PNP (Q4) transistor, then I hooked up my audio freq. generator and varied the amplitude, as I varied the amplitude the LED's came on one at a time, but they came on to fast one after another.
When I increased the freq. to 500KHz, then as I varied the amplitude the LED's came on one at a time slower the way I want them to.
So I concluded that the Mosfets are picking up voltage spikes as input signal varies, thereby charging the gate capacitance causing the output to go high and stay high longer, before shutting off.
To remedy this I placed for starters a 0.1uF, capacitor across RG1Q1, from gate to ground, to act as a speedup capacitor to discharge the gate capacitance quickly, and experimentally it worked much better, Now at a much lower freq. on the audio generator (2khz) the LED's came on slower one at a time as the volt. amplitude was increased.
So I need to experiment to find the best value of speedup capacitors, would work to discharge the gate capacitance quickly to ground. Looks like the 0.1uF works good with an actual audio input.
--------------------------------------------------------------------------------------------------------------------------------
COMPLETED succesive stages.
------------------------------------------------
I quickly put together a class A amp and biased the collector voltage to be lower than the base voltage of Q3 of the input stage so that the circuit is not prematurely triggered until a high enough signal comes in.
I hooked up my portable CD player with 100mV. output, and a spkr, to this circuit and it works nicely.
All together it works real well, all 4 LED's come on one after another in sequence in accordance to the amplitude of the signal voltage, since there are no filter circuits for this experimental circuit, then all audio freqencies modulate the system.
-------------------------------------------------------------------------
Example of hookup from input stage to second stage....ect...
---------------------------------------------------------------------------------
Design of a sound to light effects Circuit.
DESIGN:
First experiment and gather data considering the biasing of the mosfet.
" * " = arbitrarily chosen value.
--------------------------------------------------------
*VCC = 8v.
*VGQ1 min. = 2v.
*VGQ1 max. = 6v.
*VSQ1 off = 1v.
VDQ1 off = 8v.
*VDQ1 on = 6v.
*RDQ1 = 68 ohms
IRDQ1 on = calculates to be 30 mA.
RS1Q1 off... calc.to be 33 ohms.
RS2Q1 off... calc. to be 220 ohms.
*RG1Q1 = 470 ohms
RG2Q1 calc. to be 160 ohms.
*RL1 = 100 ohms.
Now some thing to consider is that when Q1 is conducting RDQ1 causes a heavy positive voltage due to the small resistance across Q1 so VSQ1 rises from 2v. to around 3v. because of the parrallel resistance between RS2Q1 and RDQ1. But since VGQ1 is at 6v. the mosfet is able to continue conducting properly.
This is breadboarded and it measures out to around 6v. at the gate, VGQ1.
Mosfet stage
--------------------------------
Now that is the voltage needed to turn the output ON. (LED ON)
Now to turn off the output (LED OFF) the VGQ1 needs to be around 2v.
Calculations are as follows.
With 2v. VGQ1 then 6v. is dropped across RG2Q1, which makes a total current of 37.5mA.
Now 2v. will drop across RG1Q1 which gives a current of 4,25mA. Therefor the remainder current will flow through Q2 which is 33.25mA. (IEQ2)
*VBQ2 = 1.5v.
VEQ2 = 0.8v.
So REQ2 calc. to be 24 ohms.
*RB1Q2 = 240 ohms ( 10 times REQ2.)
RB2Q2 calc. to be 1K ohms.
Q2 stage
-------------------
Now with the VBQ2 established at 1.5v. then the VCQ3 is 1.5v. so make VBQ3 lower for proper biasing at around 1v. That makes VEQ3 around 0.3v.
REQ3 calc. to be (VEQ3 / IEQ2) = 9.1 ohms.
Now split the REQ2 into 2 resistors with a 9.1 ohms going to Q3's emitter, and (24 - 9.1) = ~15 ohms to go to Q2's emitter.
--------------------------------------------------------------------------------------------------------------------------------
Q3 stage
----------------
INPUT STAGE
--------------------------------
Now I need to implement a PNP transistor for the inputs of the next stages, because the signal output is a negative going signal.
*RCQ4 = 1K ohms, this is to tie the base of Q3 to ground so it's not floating and keeping any eratic RF noises away from base of Q3.
*VBQ3 on = 2v.
So IRCQ4 on = 2mA.
and I'll make around 2.5v. dropped across Q4 .....*VCEQ4.
REQ4 calc. to be around 2.7K ohms.
Now that is the configuration of the succeeding stages after the first input stage.
Now I breadboarded the input stage plus 3 more of the above stages taking the output of each stage into the base input of the PNP (Q4) transistor, then I hooked up my audio freq. generator and varied the amplitude, as I varied the amplitude the LED's came on one at a time, but they came on to fast one after another.
When I increased the freq. to 500KHz, then as I varied the amplitude the LED's came on one at a time slower the way I want them to.
So I concluded that the Mosfets are picking up voltage spikes as input signal varies, thereby charging the gate capacitance causing the output to go high and stay high longer, before shutting off.
To remedy this I placed for starters a 0.1uF, capacitor across RG1Q1, from gate to ground, to act as a speedup capacitor to discharge the gate capacitance quickly, and experimentally it worked much better, Now at a much lower freq. on the audio generator (2khz) the LED's came on slower one at a time as the volt. amplitude was increased.
So I need to experiment to find the best value of speedup capacitors, would work to discharge the gate capacitance quickly to ground. Looks like the 0.1uF works good with an actual audio input.
--------------------------------------------------------------------------------------------------------------------------------
COMPLETED succesive stages.
------------------------------------------------
I quickly put together a class A amp and biased the collector voltage to be lower than the base voltage of Q3 of the input stage so that the circuit is not prematurely triggered until a high enough signal comes in.
I hooked up my portable CD player with 100mV. output, and a spkr, to this circuit and it works nicely.
All together it works real well, all 4 LED's come on one after another in sequence in accordance to the amplitude of the signal voltage, since there are no filter circuits for this experimental circuit, then all audio freqencies modulate the system.
-------------------------------------------------------------------------
Example of hookup from input stage to second stage....ect...
---------------------------------------------------------------------------------
Last edited: