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I wanted something simple and fun to breadboard and at the same time simulate in EC so this is the result. The circuits were breadboarded and functional before simulation. The xstrs were general purpose types (2n3904). The EC signal source (vccs) was a typical 940nm photodiode used in the photo conducting mode. The 7 segment display was a TIL307 (an integrated TTL BCD counter/ decoder with LED display). Because signals for the integrated display IC had to be TTL compatible, the output voltage levels of the schmitt trigger were made TTL compatible via CD4050 non inverting CMOS buffers acting as level shifters. Using TTL output levels, the high / low indicator LEDs (std 3mm/5mm) were driven directly by the CD4050 buffers w/o the need for external current limiting resistors. EC requires resistors.
For the transimpedance amp, EC simulation (done seperately) arrived at the following closed/open loop parameters at 10khz, 1) transimpedance gain 112k V/A 2) input impedance at base junction 320 ohms 3) output impedance 1.2k ohms 4) voltage gain with 1k ohm source resistance and 10uf coupling cap 86.1 V/V. 5) open loop gain 6.7 V/V. 6) None of the these parameters were measured to determine accuracy with EC, but the results are listed in the event you want to use the circuit for your own purpose. For this circuit, the quiesent collector voltage is designed to be approx 2V because increasing current output from the photodiode will only change the output voltage in the positive direction and and the lowest voltage achievable will be the quiesent level. No attention was given to looking at freq response or improving it.
For the schmitt trigger, the following results were measured : 1) Q1 off / Q2 on, Ve = 4.75V, Vc@q1 = 5.47V, Vc@q2 = 4.77V 2) Q1 on / Q2 off, Ve = 2.40V, Vc@q1 = 2.53V, Vc@q2 = 11.95V. 3) A large hysteresis gives the high/low LEDs adequate on times in the event a hi freq IR source is being detected (T.V. remote).
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