Signal amplifier circuit

Forum 2005-2010 (read only) Hardware Interfacing
#1

Hi guys

I need to build an amplifier to increase the signal from a photo diode like here http://www.picotech.com/experiments/calculating_heart_rate/index.html

I'm not that good at reading circuit diagrams yet, plus think there is a simpler way of doing it than this.

Anyone got any tips / resources?

Thanks

#2

I recommend using a device with an integrated photodiode and transimpedance amplifier like the Burr-Brown (now Texas Instruments) OPT101.

Here's a link to the datasheet: http://focus.ti.com/lit/ds/symlink/opt101.pdf

Price on this part is about $5.50US each in small quantities.

There are other manufacturers that make similar devices.

Here's a link to some of TAOS Inc's parts: http://www.taosinc.com/product_detail.asp?cateid=4&proid=18

#3

I recommend using a device with an integrated photodiode and transimpedance amplifier like the Burr-Brown (now Texas Instruments) OPT101.

Interesting, that would save me lots of hassle. Do you know if it's sensitive to infrared light?

I'm trying to decode the circuit diagram on that url on first message. What is the gap with o/p in it? There is one resistor with 120 written, but 120 what? (no units) or could that be the potentiometre.

#4

Greetings,

Interesting, that would save me lots of hassle. Do you know if it's sensitive to infrared light?

The "Normalized Spectral Sensitivity" chart on page 5 shows the peak sensitivity is 850nm with broad coverage from 700 to 1000 — yes the OPT101 is nicely sensitive to infrared.

Regards, David

#5

Greetings,

Interesting, that would save me lots of hassle. Do you know if it's sensitive to infrared light?

The "Normalized Spectral Sensitivity" chart on page 5 shows the peak sensitivity is 850nm with broad coverage from 700 to 1000 — yes the OPT101 is nicely sensitive to infrared.

I'm trying to decode the circuit diagram on that url on first message. What is the gap with o/p in it?

I have no idea what "o/p" means, but this is the output of the circuit.

There is one resistor with 120 written, but 120 what? (no units) or could that be the potentiometre.

Resistors are always in ohms unless otherwise indicated with a "K" for thousand ohms or "M" for million ohms.

Capacitors are in farads unless otherwise indicated, but a 1F capacitor is so huge that you'll never see it in normal circuits like this.

Regards, David

#6

Hi guys

I need to build an amplifier to increase the signal from a photo diode like here http://www.picotech.com/experiments/calculating_heart_rate/index.html

I'm not that good at reading circuit diagrams yet, plus think there is a simpler way of doing it than this.

Anyone got any tips / resources?

Thanks

Actually if the bandpass filter and the gain of 10,000 are both important to you this is a pretty minimalist circuit.

Regards, David

#7

I am having trouble finding a UK supplier for an OPT101.

I think I found one on Farnell
http://uk.farnell.com/jsp/endecaSearch/partDetail.jsp?SKU=558965

But then it looks completely different to the one on Ebay US, so I dont think its correct.
http://www.sage.lunarpages.net/wfc/DIopt101.jpg

Any thoughts?

#8