Digital Anemometer

[Vizier87]

Can someone please explain this circuit:
**broken link removed**
I am only familiar with transistors which is common-emitter for switching purposes, but the placement and connections of the resistors and op amps is quite confusing.
My main confusion:
What's the use of the 2n3904?
Do other transistors work for the ones for differential heating?
Why do we use integration config for op A1?
Thanks.

 

[BrownOut]

Without doing a detailed analysis of your ckt, I'd say the 3904 is there to correct for the logarithmic output of the other two transistors. Q1 and Q2 use their temperature dependent characteristics to measure air flow. The air passing over them cools them, and affects the junction voltage.

Is there an article that goes with this diagram?

 

[Willbe]

king's law anemometer - Google Search

 

[BrownOut]

king's law anemometer - Google Search

Gurggle wasn't very helpful here.

 

[ccurtis]

The originating article is at this link:

**broken link removed**

"...Q3 acts with A2 to limit the maximum voltage across R1 to about 2 V. This is done to avoid the risk of latch-up, which would occur if A1's output were allowed to rise too near the 5-V rail."

 

[Vizier87]

Thanks for the tip.

 

[Vizier87]

Hello guys.... I'm building this circuit (post #1) already and was wondering on how do we configure the values for R1,R2 & R3 to adjust the anemometer's airspeed range sensitivity? This circuit is in accordance with the link to the article about this posted in the replies.

 

[Vizier87]

knock knock.