A2 ELEC6 CW - Part 3

Dec 13, 16 - 17:15pm, 1 year and 6 months ago

Back again a week later, here’s another update on what I’ve been up to.

• Redesigned most of the circuit
• Re-built the photodiode array
• Found out something cool about lights
• Wrote some code
• Started on the LaTeX document

Rethinking the circuit

I spent a few hours over the week to rebuild the circuit in Yenka;

So what’s changed? \

• I changed the phototransitor array from using 311N’s to 741 op-amps.
• Created a logic system so to stop TR1/TR2, or TR3/TR4 being on at the same time (which would destroy the MOSFET’s).
• Generally simplified the system, removing unnecessary components.

Rebuiling the photodiodes

Basically, the whole array was wrong; to start off I couldn’t get the 311N’s to work as comparators properly, and the circuit I was using was supposed to amplify the output voltage of the photodiode, it didn’t have a very large $V_{gain}$ so I decided I didn’t really need it. Instead I’ve just implemented a simple comparator using 741 op-amps.

When I got the phototransistors working, I found out that they didn’t switch from high/low immediately. I wired up the output of the comparators to some LED’s and saw that the LED’s light faded on/off, which is very odd since, $V_{out}=A(V_+-V_-)$, therefore any slight difference in voltage is amplified (limited to the supply), so in theory Vout should’ve gone from +Vs instantly.