I use R4 just ~270 Ohm for chip BL-L512PD photodiode. When R4 will be lower than required, you will be have very clear signal from ST-7L but highest level will be below your reference voltage (VCC/2) on input 6 IC1B and signal form ST-7L will be not recognized yet! If your reference voltage will be near 1-1,5 V that you will be able receive very clear signal from ST-7L with high level above 1V and no any missed 'bits' on RX line or unstable connection. If value for R4 will be little bit higher than required value, than you will have enough amplitude on output from ST-7L (in direct input 5 on IC1B) for recognizing signal presence, but all short peaks will be pulled up to high level and can not be recognized by IC1B. This item: Fluke IR189USB USB Cable Adapter 7695 Fluke - FLUKE-IR3000FC IR3000FC Infrared Connector for Connect 12907 Fluke 287 True-RMS Electronics Logging Multimeter 60319 Total price: 809.21 Some of these items ship sooner than the others. With 5V VCC not easy to pick up right value for R4. Photodiode have internal capacitance that can be reduced only with high backward voltage. From Fluke, cable comes with a drivers CD, but. That make your scheme unstable, ecpessially when you use photodiode with low photocurrent (2-10 μA).įind great deals for Fluke IR189USB USB Cable Adapter for Fluke-189 DMM's. I not understand why you choose VCC/2 reference voltage. That will give you 1V reference voltage on inverted inputs LM393. In R2/R3 divider I suggest you change R2 from 12K to 3K. In FT232R all input pins are pulled to VCCIO via internal 200kΩ resistors. You need exclude R5 resistor from RXD line. Anonymous Some notices about your schematic.
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