Figure 1
Just to explain- the gyrator circuit is acting as a constant circuit. It has a time constant such that it cannot react fast enough to my incident signal (10us pulse). The current signal (low pulse) is then converted to a voltage signal by the AD817AN used in trans-resistance configuration (or trans-impedance as sone like to call it - dont know which one's right).
TroubleShooting:
Tried to do some trouble shooting. Found the base of the transistor in the gyrator circuit(R1, Q1, C1, R2) was not stable. Tried increasing C1 to 470nf to help fix this.. but still have the same problem,.
Also noticed C2 had a time constant associated with it.. with the same response as at C1 (refer figure 3- 2nd response). So tried increasing C2 to 1uf (non-polarised C), but still of no avail.
SO when the signal is near- clean square wave - can see C2 charging and discharging. ( figure3)
As signal gets further - ringin at edges - response at C2 is almost a flat line ( figure 2)
any ideas as to wot is causing this problem?
Trans-reactance Output at 5cm distance
Figure 2- Trans-reactance_output; C2 response; 5cm dist
Trans-reactance Output at 0cm distance
figure 3- Trans-reactance_output; C2 response; 0cm dist
Useful Links
BP104- photodiode http://www.jaycar.co.nz/products_uploaded/ZD-1947.pdf
AD817An- http://www.datasheetcatalog.com/datasheets_pdf/A/D/8/1/AD817AN.shtml
Contact
electronics amateur: generous.boy@gmail.com