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I simulated these in LTspice **broken link removed**
The fix #1 shows 1.5v at output
fix #2 shows 1.3v at output.
Looks like I am back using the 741 op amp using fix #1
Most of the circuits that work well use the photo-transistor with gain so its output is from its collector and its collector resistor value is high. But then it needs to drive an amplifier with a high input impedance like the input of an opamp. The opamp can also have as much gain as you want. Then the opamp drives an LM386 power amplifier that drives a speaker or headphones.
The last circuit you posted has the photo-transistor collector resistor value only 1k to 5.7k (instead of 100k to 1M) and it feeds the fairly low 10k resistance of the volume control instead of feeding the many meg-ohms input impedance of an opamp.
The circuit is also missing the important 10 ohms resistor in series with a 47nF capacitor to ground at the output of the LM386 and is also missing the very important 100uF and 0.1uF capacitors across the battery.
If a transistor replaces the opamp then the low input impedance of the transistor kills most of the output from the photo-transistor, which is why one of your circuits used the photo-transistor as an emitter-follower that has a low output impedance but has no gain.
What are you using to provide a modulated light source? Maybe it is not modulated enough.
I tried using florescent light which worked using the op amp.
The transistor circuit worked but you can barley hear it (a remote control as light source
I know I am missing the resistor/cap to ground on the output but that shouldn't make it louder for test purposes.
In the final design I plan to put the cap/resistor (my pcBoards don't have it but then the circuit doesn't really work well so junk)
I had a crazy idea = use the photo transistor to trigger a 555?
Looked for a lower voltage op amp but most are either smd or 14 pin.
The opamp in your new circuit will not work. You have its power supply pin 4 not connected to a power supply.
Its datasheet shows than pin 3 must be at least 3V more positive than pin 4.
Since pin 3 is at ground then its negative supply pin 4 should be connected to a negative 9V battery.
Or pin 4 can be connected to ground and a voltage divider can make pin 3 at half the supply voltage so then the opamp can pass audio signals.
You have the opamp inverting so it has a low voltage gain of only 10. If the opamp is non-inverting then it can have a nice high voltage gain.
What is the value of C3?
An MC33071 or MC34071 single opamp will work from a supply as low as 3V. They have the same pins as a 741 opamp.
I missed the red 9- in this fix #1. Now I need to maybe reconfigure as I am using ONLY one 9v battery **broken link removed**
Will look at the MC32071 and MC34071
seeing how it has two in one package for $1.9 might as well utilize?
Here is a schematic I found Looks promising?
using the moc205 as photo transistor?
An MC34071 is a single (mono) opamp. It costs $1.05 each for thru-hole at Digikey today.
An MC34072 is a dual (stereo) opamp. It costs $1.09 each for thru-hole at Digikey today.
Your first opamp has such a low input impedance (because it is inverting) that it shorts the output of the photo-transistor.
Here is an inverting opamp and a non-inverting opamp:
While running an errand for the breakfast this weekend it dawned on me
The LM741 circuit worked EXCEPT it needed a split supply at 9v each rail
If I use the suggested MC33071 then we should be good to go??
HOPEFULLY
back to square 1 Right Church, wrong pew
Your opamp WILL NOT WORK because NO opamp will pass audio when its (+) input (pin3) is at the same DC voltage as its (-) power supply pin (pin4) like yours is.
Because then it inputs do not work or its output is as low as it can go and it becomes a rectifier.
Pin 3 MUST be biased at half the supply voltage which is ground when there is an additional negative supply.
The MC33171 is rare and costs a little more than an MC34071 which is more common. They both operate from a single supply that is as low as 3V and their maximum allowed supply is 44V.
The MC33171A is even more rare and costs more than an ordinary MC33171.
Your first opamp does not have any DC negative feedback so its output will be saturated high or low depending on how much ambient light shines on the photo-transistor. A saturated opamp does not amplify.
Your first opamp is inverting so its voltage gain is only 1M/100k= 10 (if it had some DC negative feedback).
I think the first opamp should be non-inverting. Then it can have as much signal gain as you want.
here are the plots from LTspice
I assume that with 9v input it will saturate the op amp.
The left schematic are what I was using for the LM741 that I got from the Forrest mimms book
see post # 1 I think?
No.
When the photo-transistor in the first circuit has some ambient light then it conducts and its output DC voltage drops.
The photo-transistor has an output voltage from almost 0V when the ambient light is bright to +9V when the ambient light is not bright. The opamp amplifies it 200,000 times so its output is saturated low or high. Then the opamp is not an amplifier.
The second circuit has 100% DC negative feedback so its output DC voltage is always +4.5V and it can swing up and down with the signal.
EDIT: Your Spice circuits do not have an ambient light and also do not have a modulated light signal.
EDIT again: The negative feedback resistor is 1M (one million ohms), not 1m (one thousandth of 1 ohm).
The capacitors are filters that are important when the battery runs down and develops a high internal resistance.
C6 filters the battery voltage to prevent it from jumping up and down when the current decreases and increases with the signal.
C8 prevents the DC bias voltage from jumping up and down when the current decreases and increases with the signal.
Your input opamp is inverting so its voltage gain is only 10 which might not be enough.
What is the value of the output capacitor C3?
What is the speaker impedance?
The D in the part number of the opamp is for a tiny surface-mount case.
Speaker is 8 ohm
The capacitor I believe is .047
will recheck the tda2822 supposed to be a dip as young just learning to solder boys are to assemble. could be the designator in the Diptrace program but the pattern shows 8pin dip after I attached it to the symblo.
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