12f675_fuse_about_to_blow!

[LEDave]

Quick question:

When does an INPUT voltage level on a pin become an INPUT? What I'm clumsily trying to say is that when I use my potential divider (fixed resistor and an LDR) the voltage level will gradually rise until the PIC reads that voltage as a logic 1, will that be exactly five volts or less?

Dave

[mackrackit]

If you are still using the 684 take a look at table 15.5 in the data sheet.
There are two types of inputs, schmit and TTL. One is 0.8 and the other is 2.

How is everything going with the project?

[LEDave]

Hi mackrackit,

If you are still using the 684 take a look at table 15.5 in the data sheet.
There are two types of inputs, schmit and TTL. One is 0.8 and the other is 2.

Yes still on the 684, I'll have a read of the data sheet tonight.

The Project is coming along, I love these PIC's and what they can do (still frustrated at what I can't do mind) When you start a project it's amazing where things lead and what has to be taken into account, example:

The parent birds fly into the box bringing in food and each time they do so they break the beam and a counter (divide by two as we said earlier) gets incremented. Then as night falls the voltage level on the P0T_Divider rises and when it's dark a pin reads voltage 1 and that days data gets rfpic'ed across. However simple little things to consider, how dark is dark? Is a passing cloud 'dark' enough to make the data be sent prematurely etc...? Things like that.

I've been spending time analysing Bruce's rfpic program to try and figure out just what is going on and how it all works. Plus I've been dabbling with some basic assembler...oh dear

It's a good job I've got until next Spring to get this up and running Also learning to program is a great thing to go over the Winter Months too.

So, slow progress, still loving it.

Dave

[LEDave]

I'm probably way of beam here but when I read the data sheet for the 684 and then read about the 'Schmitt Trigger' it seemed to me that this worked on a pre defined voltage level (the voltage can vary up to the set value). Maybe this could be the way to ensure that any data sent only gets sent at a 'set' light / voltage level.

Am I reading this right?

I know I could also just use the potential divider set to a voltage / light level and even add in a time delay routine (say an hour) to make sure the data only gets sent once and when it is dark.

Interesting though.

Dave

[mackrackit]

I hope this makes sense..

At around 5 vdd.

A TTL input pin will go "HIGH" around 1.1 volts. 1.1 volts is the ON?OFF threshold.

A Schmitt input will go "HIGH" around 3 volts but stay high until it drops below 1.6 or so.

Your meter may vary a bit. Mine does

Personally in an application I will not call an input high before 3.6 volts and LOW has to be 1.5 or less. This is dealing with limit switches and such. Basically I figure it is either on or off, Dirty contacts, bouncy switches and such adds to the problem.

If I need to split hairs (volts) I do not like to rely on TTL or ST for the threshold. I set up an ADC.

[LEDave]

Interesting,

If I need to split hairs (volts) I do not like to rely on TTL or ST for the threshold. I set up an ADC.

Well I've never done ADC, it does look an ideal application for the project and new learning for me.

When you have some spare time (spare time, as rare as hen's teeth he says) could we do some ADC stuff? No rush, as and when, as ever.

Dave

[mackrackit]

When you have some spare time (spare time, as rare as hen's teeth he says) could we do some ADC stuff?

Sure, I have been planning to write some some basic ADC stuff for the wiki so I will use the 684 as one of the example chips.

But in the mean time you can not beat this foe an explanation. Different chip but most still applies.
http://rentron.com/PIC12C67XAD.htm