I guess this is a direct question to Paul, nevertheless I thought it would be proper to ask it here and not send a private email.
I am currently trying to design a flame sensing circuit so I was very happy to find this article and I try to use the information in it as the basis for my design (https://www.pjrc.com/pilot-light-flame-sensor-for-burning-man-art/).
Actually I am interested in the AC generation + flame sensing section only without the ignition and valve control.
However there is something that I seem not to understand in the AC generation section - since there is no schematic in the article I used the PCB Gerber to understand it, so I could have missed something.
My circuit is 24V based but I think that this should affect the design only marginally (maybe only the transformer ratio).
I intend to generate the sine wave using a pair of op-amps - one acting as a square wave generator and the second as a LPF - so this would replace what was done in the article design with the Teensy DAC + low pass filter + opamp.
This sine wave will go into the transistors pair buffer as in the article.
Now comes something that was not mentioned in the article and I am not sure if I understand it:
The transistor buffer output goes through a series connected 100 uF capacitor + 10 Ohm resistor into the transformer - I assume that this is in order to create an AC coupled circuit so that the resulting AC will ride around 0V (otherwise, I guess, the whole rectification phenomenon is useless, especially since both sides of the transformer share a common ground). Also, if I understand correctly the transformer is installed with the primary facing the output.
However when I run this circuit in a simulator (Tina-TI) I get at the input to the transformer voltage signals that make no sense - attenuated and distorted instead of amplified (obviously the transformer output follows these signals) . This could be due to improper parameters to the simulator (most probably the transformer), but I would like to make sure that I did understand correctly.
I also noticed that the same output also feedbacks to signal generator opamp via a 100K resistor, which is something that I did not understand either.
Could you please clarify the AC signal amplifying?
Thanks
I am currently trying to design a flame sensing circuit so I was very happy to find this article and I try to use the information in it as the basis for my design (https://www.pjrc.com/pilot-light-flame-sensor-for-burning-man-art/).
Actually I am interested in the AC generation + flame sensing section only without the ignition and valve control.
However there is something that I seem not to understand in the AC generation section - since there is no schematic in the article I used the PCB Gerber to understand it, so I could have missed something.
My circuit is 24V based but I think that this should affect the design only marginally (maybe only the transformer ratio).
I intend to generate the sine wave using a pair of op-amps - one acting as a square wave generator and the second as a LPF - so this would replace what was done in the article design with the Teensy DAC + low pass filter + opamp.
This sine wave will go into the transistors pair buffer as in the article.
Now comes something that was not mentioned in the article and I am not sure if I understand it:
The transistor buffer output goes through a series connected 100 uF capacitor + 10 Ohm resistor into the transformer - I assume that this is in order to create an AC coupled circuit so that the resulting AC will ride around 0V (otherwise, I guess, the whole rectification phenomenon is useless, especially since both sides of the transformer share a common ground). Also, if I understand correctly the transformer is installed with the primary facing the output.
However when I run this circuit in a simulator (Tina-TI) I get at the input to the transformer voltage signals that make no sense - attenuated and distorted instead of amplified (obviously the transformer output follows these signals) . This could be due to improper parameters to the simulator (most probably the transformer), but I would like to make sure that I did understand correctly.
I also noticed that the same output also feedbacks to signal generator opamp via a 100K resistor, which is something that I did not understand either.
Could you please clarify the AC signal amplifying?
Thanks
