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IR trip wire with discreet components Answered

I am in need of help and I am going insane with this. Question is about a simple circuit with IR sensor/tripwire part and 555 timer which would keep the alarm buzzer on for thee seconds. No fancy stuff like arduino or relay or anything like that just LEDs, resistors, transistors, 555 timer and a buzzer.

I got the IR sensor part to work and the timer part to work, but when I try to combine them everything goes haywire and nothing works.

I have IR photo transistor TOPS-030 as the IR sensor. I am really starting to lose my mind with this and it has been three years since I started doing this project. I got diagnosed with undefined neurological disease (probably MS-disease) which has slowed my down even more. I worked on the circuit every now and then not every night during the past three years =)

I know this circuit is simple and it can be put together in a brief moment the thing that is driving me crazy is the fact that when I got something working then everything goes haywire. Doing very basic beginner instructable describing this circuit would be very helpful even to others not just me. It would also keep the knowledge of using discreet logic up in these micro controller days.

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msiren

2 years ago

One thing that I wonder is that what might be possibly wrong when the range I get from the IR phototransistor is something like 10cm. The circuit that I had put together which had the same problem until I did something (I thought I put the transistor other way around) and got a really good range with it. I tried constructing simple circuit with vcc (9v) going to the phototransistor and after that parallel connection as output and 10k going to ground, the resistor and output was after the transistor to get the output signal suitable for 555 meaning when the IR beam is broken the output signal goes low. This had the same issue that I had before only approx 10cm range on the IR. The obvious answer is that the IR led is too weak, but that would not explain the situation when I got well over a 1m range with the same IR led and the same resistor and same power source that part hasn't changed in a long time.

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msiren

2 years ago

It appears that this circuit is impossible to build. I would have imagined that experienced person in electronics could have build this up from a scratch but appearantly it is impossible. I tried this very very simple photo transistor circuit and it appeared to work with veeery low range around 10cm, but when connecting the output to a 555 timer trigger nothing worked again. I have given up on this because it is impossible to do without micro controller or relay or some more "exotic" like that.

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caitlinsdad

2 years ago

I dunno, you may need to throw in some things like capacitors and diodes. What circuits do you currently have set up?

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msirencaitlinsdad

Reply 2 years ago

The attached picture is quite close what I had put together. D2 acts as the IR photo transistor, D1 is just generic red led and might have some other oddities if some component (specific led) is wrong way around in the schematic they have not been on the circuit. I tried to follow https://www.instructables.com/id/Infrared-IR-tripwire-module/ which instructed the 100k pull-up resistor which is probably fine when you want logic level signal. To compensate this I tried putting the 10K on the vcc going to 555 so that the trigger high signal would be quite close to the vcc level meaning that the low signal would be 1/3 vcc. If I would have put 9v directly to the 555 then it would see 3v and below as low signal and the pull-up resistor made it the trigger signal to be around 2v in high state,

tripwire.gif