Greetings,

I am finally getting around to building the circuits found in my Forrest Mims books purchased on eBay. Currently I am building the AM Lightwave Transmitter circuit. In the process of discovery, I've found that the LM741 is dated and therefore it seems people point to the OPA134. So I have ordered some of those as I continue to experiment and build this circuit out and learn from doing so.

Question: The AM Lightwave Receiver circuit (shown in image) shows the use of an LM741 once again. Would this also be a suitable scenario to replace with the OPA134? Will there be a strange interaction using along with the LM386? I don't fully understand why both would have been used to begin with. Perhaps the LM741 is a preamp?



I really look forward to hearing some feedback (pun not intended... or maybe it is) from the community. Has anyone else ever built this circuit out and used it?

Cheers,

Coach

 

Hi CT,
Welcome to AAC.
That OPA134 should work OK.
How do you plan to drive the opto receiver with light?
E

 

How do you plan to drive the opto receiver with light?

If I am understanding your question correctly... Not quite. It would appear per the inserted image above, that I will be needing to source a phototransistor for the RX'er circuit. In that vein, light drives the gate...

 

Coach.
Use LTspice with my model library. It has operational amplifiers 741 and 134. There is a link to my libraries on the forum. And yes, the operational amplifier is used as a pre-amplifier. A 1-mOhm potentiometer can be used with 134.

 

Hi CT.

The preamp OPA134 is AC coupled, which suggest a pulsed light source.
E
A quick sim of the preamp.
E

 

Hi CT,
This is full simulation of your circuit,
E

 

This is full simulation of your circuit,

That is pretty cool. I've read that the OPA134 doesn't require a dual rail supply and can happily be supplied +5V which is another appealing aspect of that IC. Most electret condenser mics I've found are happy with +5V rather than ± 9V.

Yesterday, I started with the first part of this project and that was to learn how to bias the ECM. I connected a 22k ohm resistor and 0.1uf capacitor to the input side of the ECM and the other side to ground. I was quite happy with what I saw on the oscilloscope. So I switched the 22k ohm resistor out with a 50k ohm potentiometer and adjusted the setting to see the gain results on the oscilloscope. Quite cool.

Seeing this use of LTSpice looks neat also. I just never found the time to install and learn it. I used Simulink while I served in the Air Force for a couple of things. I do see the value in simulation.

Thanks for all the inputs thus far... When my OPA134 and Phototransistors arrive in the mail I will begin testing.

Cheers,

Coach

 

Hi CT,
When using a single supply of +5V, you will have to modify the circuit to suit.
This LTS simulation is an example.
Final values will depend upon the type of photodetector used and also the specification of the remote light driver and signal.

E
OT:

Simulink while I served in the Air Force

I served in the R.A.F. Ground Radar 1950-55