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Offline typedef

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Interrupt voltage level
« on: June 05, 2016, 01:09:41 AM »
hello
I bought the parts and managed to create the sensor. The first time I did it, i used jumper cables and an arduino board and was able to see midi notes in the serial monitor.
A few weeks later, I decided to cleanup the breadboard and switch to using wires and things stopped working

1- the LED is still flashing like it used to
2- now the maximum voltage at pin 3 of the 555 timer is at 2V. I didn't measure the max voltage before the cleanup :(. Is the voltage to low to trigger a rising edge? Is it supposed to be at 3.3V with 5V Vcc?

I used a simple Arduino sketch to verify that my connections were working, and indeed I can read the voltage from the timer.
I used a multimeter and everything looks good. even measured the capacitance of each cap and the resistance of the 100k. everything is in order.
I can attach a picture of my circuit if it helps

thanks!


 

Offline sam

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Re: Interrupt voltage level
« Reply #1 on: June 05, 2016, 10:04:54 AM »
You are correct, 2V likely will not break the rising edge, how are you powering the 555 timer - just off the 5v out of the arduino?  Make sure you are giving the 555 a full 5v (4.7).


Offline typedef

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Re: Interrupt voltage level
« Reply #2 on: June 05, 2016, 01:20:18 PM »
yes, but its seems that sometimes the Vcc is dipping below 5V, around 4.6 or so.
seems that the pot I am using is causing that, its the 10K trim pot https://www.adafruit.com/products/356
also, I rewired some connections by moving them closer to the 555 timer pins on the solderless breadboad and it got a little better? \
the rate of interrupts is not as high as the LED flashing, it goes above 2V but not reliably...?
thanks for confirming though, i'll keep digging :)
 

Offline typedef

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Re: Interrupt voltage level
« Reply #3 on: June 05, 2016, 01:26:29 PM »
hmm, seems like having a leonardo and an arduino (and other peripherals) plugged to the usb hub is not ideal ... that seems to be it.
I guess the arduino board was getting a tad less than 5V and hence everything was a tad lower? lesson learned!
The voltage is now at 2.2V. yay!

Offline typedef

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Re: Interrupt voltage level
« Reply #4 on: June 05, 2016, 02:32:00 PM »
well, i was a little hasty. The USB argument might be relevant, but something else is going on.
I plugged the arduino baord directly to the computer and ran a simple sketch that reads the 555 timer on A0.
With the LED plugged in,  I get a  value of 425, without it 1023. Vcc is 5.04V. So i have voltage drop somewhere.
is it the caps? did one them burn out?   

Offline sam

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Re: Interrupt voltage level
« Reply #5 on: June 05, 2016, 05:01:24 PM »
If the LED is flashing, then the galvanometer circuit should be working.  Here is another point, what specific 555 timer are you using?  i prefer the LMC low voltage version (used in the sprout)  where a 555CN or LM555R might require more power.

If you are tapping off the Leonardo's 5v line, then the regulator onboard is doing all the work, i see no reason that the interrupt wouldn't be reading the low pulse.

Oh in your code, are you "pulling up" the input pin?  yep, gotta do that cause we read the 'falling' edge of the 555 pulse. 

Offline typedef

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Re: Interrupt voltage level
« Reply #6 on: June 05, 2016, 08:48:19 PM »
i am using the TLC555, which seems suitable for this application?
http://www.ti.com/product/TLC555