Sensors

x: 10ms/div y1: 200mV/div y2: 1V/div Taken from here and using a 10x probe. y1: sensor voltage (minus offset) y2: amplified and stretched

I'll try to use this as a position sensor for one of the brake cables on my bike. Thought of strain gages or hall sensors to sense the tension in the cable, but this seems to be the cheapest way to do it. Position doesn't really map 1:1 with tension (= braking force), but it will be close enough to use it.

I'll try to use this as a position sensor for one of the brake cables on my bike. Thought of strain gages or hall sensors to sense the tension in the cable, but this seems to be the cheapest way to do it. Position doesn't really map 1:1 with tension (= braking force), but it will be close enough to use it.

I'm still using my old scope ;-)

As the 8pin LM2940 op-amp is a dual amp, I've distributed the amplification to both amps. The first stage still adds an offset and has adjustable amplification, the 2nd stage is a fixed at a factor of 11. I've also added a low-pass filter at the output to smooth the signal some more. C5 was added for AC coupling and must be at least as big as C1. D2 was added to allow C5 to be discharged and be ready for the next pulse.

LM2940 non-inverting amp, no pulse stretcher yet. All this amplifier business is a black art of its own. In retrospect I must find that all the lectures I've taken at uni regarding electronics were only capable of teaching the very basics, if at all. I didn't study EE though, but some other natural science which is highly unpopular among most people, especially at school. And I still don't know sh*t about you name it. So much to know, so much already forgotten.

The white push button switch triggers the staircase lights. I close the circuit with a small reed relay. As I couldn't make any sense of the wiring, I added a "rogue" wire from the doorbell switch. It provides 13.8V AC with enough current capability. The installation manual of this com system is quite terrible for people wanting to understand how it works. It only contains wiring examples for all the different setups you can choose from, but nothing substantial as to what the wires may do (which is power, which is signal...).

A single supply non-inverting amp with pulse stretcher. It's also got an offset 'knob'. The LM2940 is a dual amp, so maybe I'll add some more pulse shaping. It sucks that all the easy stuff requires symmetric supply voltages. But using just 5V also means that there won't be any over-voltage or negative voltages that could kill the AVR. The blue curve will be integrated by a microcontroller.