Input question from a newbe

[Bdlhome]

Update and further question:

I'm sensing the state of 6 LED's using the resistor approach which a great with 5 out of the 6 LEDs. I'm using a resistor of great enough value not to light the LED.

The problem with one of the LED is that the sensing is unreliable (sometimes it would read the LED coming on and sometimes it wouldn't). Using a meter I found that when the problem LED was on the voltage was ~1.2V at point 2 of the original diagram where the other 5 were at close to zero. It is strange because all 6 LEDs are in the same circuit. The issue appears to be that the PIC sees the ~1V as high which makes sense.

I did tried the lm78L05 to92 approach but couldn't stop it causing the LED to be illuminated when the LED was off.

Any ideas?

[Bdlhome]

This forum is magic, I ask a question after spending hours trying to fix something and then within an hour I come up with an answer. The answer appears to be use a 5v zener diode is series with the resistor.

So my next question is what is next weeks lottery numbers?

[mister_e]

The one I have

[Bdlhome]

Not expecting an answer from Steve because he should have collected his winnings by now

For everyone else; I want to track when a switch (which is in an existing circuit) is pressed and was hoping to use the same approach. The problem is the voltage is 0.7V when push to make switch is open and 0V when closed and that doesn't appear to be enough of a range.

[mister_e]

ADC, comparator?!? Arwe you sure it's just not a sort of open collector output you have on hand? What if you attach a pull up resistor to it.

In meantime i'll count my millions

[isaac]

Not sure what you are trying to do but 0.7v is quite low
but if that's what you are measuring and assuming its the correct voltage why not fed it via an op amp then adc

[mister_e]

the adc is capable to do the job without the opamp in this specific case though.

(0.7/5)*1023=143
(0.7/5)*255=36

[HankMcSpank]

For everyone else; I want to track when a switch (which is in an existing circuit) is pressed and was hoping to use the same approach. The problem is the voltage is 0.7V when push to make switch is open and 0V when closed and that doesn't appear to be enough of a range.

Probably better for you to define track for your "0.7V" being presented to the PIC....

1. Immediately being notified when the switch is pressed? - use a comparator with PIC's comparator interrupt.

2. hopefully catching someone pressing a switch while polling the ADC Result very frequently? - use ADC and a tight main loop.

[Bdlhome]

Probably better for you to define track for your "0.7V" being presented to the PIC....

1. Immediately being notified when the switch is pressed? - use a comparator with PIC's comparator interrupt.

2. hopefully catching someone pressing a switch while polling the ADC Result very frequently? - use ADC and a tight main loop.

Both would probably work, although #1 is probably better for my project. Having said that, I'm using this project as a learning experience, so I will try both.

Thanks everyone