Calling electronics gurus

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mzplcg
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Calling electronics gurus

Post by mzplcg » Sat Jul 01, 2017 4:39 pm

OK, my electronic engineering days were over 30 year ago and it's failing me for what should be a simple task.

What I want to do is amplify a signal from a crankshaft sensor into a usable signal at TTL levels. The output is about a volt, so not high enough to trigger a CMOS chip. So I need an amplifier before the CMOS input stage but i'm buggered if I can remember the best way of doing it.

I was thinking about using a FET, using a voltage divider on the input to get the gate to within 0.5v of trigger point and then the output from the crank sensor should switch it, but then I thought about an Op-Amp type of thing perhaps, or maybe even a straight voltage divider on the inut of the CMOS to hold the pin just below trigger voltage so it can actually do something with the sensor output......

Help please. Quickest and easiest way to turn a 1v DC pulse into a 5v DC pulse or square wave.

Ta.


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Re: Calling electronics gurus

Post by benp » Sat Jul 01, 2017 9:24 pm

... FET ? honestly I dont know is the short answer


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Re: Calling electronics gurus

Post by anglefire » Sun Jul 02, 2017 7:45 am

Dom,

Unless someone comes up with a answer in the meantime, I'll ask school friend of mine - as, like you, my electronics days are well behind me! He still does stuff in machine code, and proper electronics so will have the answer.


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Re: Calling electronics gurus

Post by mzplcg » Sun Jul 02, 2017 8:31 am

Perfect, thanks Mark


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Re: Calling electronics gurus

Post by PillowSmuggler » Tue Jul 04, 2017 1:05 pm

Sorry Dom, I too am way too out of practice with my electronics.

Best I can do is :
Schmitt.JPG
Which I got from here using the calculator feature to play with values till I got into the 1V detection range :

http://hyperphysics.phy-astr.gsu.edu/hb ... tt.html#c3" onclick="window.open(this.href);return false;

Do you have a scope output to show how the signal is shaped? It would help refine the gate range for the detection.

Note that the Schmitt output is inverted so 0V when the input triggers, and will require flipping if you need a positive output.


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Re: Calling electronics gurus

Post by mzplcg » Wed Jul 05, 2017 8:48 am

Cheers Dom. Yes I have a scope, ancient though it is the thing does work.

So, I got something similar which I hacked together from a few sources. Presumably your circuit uses an op-amp, or a Schmitt trigger version of it - I am using a good old 741 Op-Amp. Yours (using that pin config) seems to be an inverting output although if the input is connected to pin 3 instead of pin 2 it becomes non-inverting. I do like the Schmitt trigger idea though as it becomes a pulsing switch rather than a pure amplifier so there is less likelihood of a vague output.

This is what I got to. With the resistor values of R1 and R2 I should get a gain of about 10, noting that R1 should be 5k6 using the formula
Gain = 1+ (R2/R1)

Image


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Re: Calling electronics gurus

Post by PillowSmuggler » Wed Jul 05, 2017 12:49 pm

Dom,
Yes my circuit was a standard 741 op-amp also; the feedback resistor R3 makes the output slam each way making it behave as a Schmidt trigger with hysteresis.
You can use a standard packaged Schmidt after your amp circuit, though using an op-amp like mine allows you to skew the trigger values more easily (and would require an inverting Schmidt at the output to make the output positive).
If the output pulse width needs modifying, consider a 555 timer in mono stable mode with the reset driven by the output.
Or if you're feeling like taking on the brave new world, take a look at picaxe single chip microprocessors, which can do all of this with simple code or even a simple flowchart design. They're based on a microchip pic, but with a very basic o/s loaded that allows primary school children to build and upload working designs - happily this also makes it easier for us adults and the support hardware is cheap as chips. http://www.picaxe.com" onclick="window.open(this.href);return false;


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Re: Calling electronics gurus

Post by mzplcg » Thu Jul 06, 2017 12:16 pm

Well, I built that circuit and it works like a champ :thumbright:

Interesting stuff on that picaxe.com though. Some decent ideas on there.


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Re: Calling electronics gurus

Post by PillowSmuggler » Thu Jul 06, 2017 5:58 pm

I had built an automatic water level controller with a picaxe; using 4 stainless steel rods (two long, one slightly shorter at the low level mark, one short to detect high water).
Pushing 4khz 50% PMW down one longest wire and then looking for the signal on the other three it then figures out if there's space in the tank for more water and turns on a solenoid for a max 30 seconds or until high level reached. If no signal detected on the other longest rod it just shuts down. Once it's gone 30 seconds without a change in state it locks out until a power cycle in case the sensor has become disconnected or there's a leak in the tank.
Total cost was under £20. I have a lot of respect for the flexibility of a picaxe :thumbright:

Shame it got fried during a thunderstorm when the plug transformer exploded :oops:


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Re: Calling electronics gurus

Post by PillowSmuggler » Thu Jul 06, 2017 10:38 pm

Now you have a working circuit (Well done :thumbright:), what are you going to drive with it Dom? A tacho dial or something?


Regards, Dom.
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