Crystals

[jason]

Hello ya all

I am trying to implement a battery backup and a low power mode when theres no power. I just need to detect a door opening and record the time and date to a serial eeprom.

When I looked up the pic I'm useing I was happy, only 500 Na in standby but when I looked up the crystal oscillator I'm using it said 20ma

I have always used these type of oscillators due to solid performance and not needed the hard to find caps. But this project is all SMD and needs to be low power while the machines turned off all night. Sooooo

this Pic is the PIC16F59-I/PT running at 20mhz (but 4mhz would work fine).
How many mili amps or N amps would a normal crystal with caps use ? and would I define LP crystal ?

[skimask]

I am trying to implement a battery backup and a low power mode when theres no power. I just need to detect a door opening and record the time and date to a serial eeprom.
When I looked up the pic I'm useing I was happy, only 500 Na in standby but when I looked up the crystal oscillator I'm using it said 20ma
I have always used these type of oscillators due to solid performance and not needed the hard to find caps. But this project is all SMD and needs to be low power while the machines turned off all night. Sooooo
this Pic is the PIC16F59-I/PT running at 20mhz (but 4mhz would work fine).
How many mili amps or N amps would a normal crystal with caps use ? and would I define LP crystal ?

I got different numbers than what you got...(according to DS41213D)...
@ 20Mhz @ 5v, using a crystal, running (not including any external pieces/parts, extended temp version) - 7mA max
Standby/Sleeping - 2v w/ WDT enabled - 15uA max.

Any reason why you're using the 'F59? There are much better chips out there with a lot more options and probably cost the same, if not cheaper. The 'F59 doesn't have much in the way of options.

[jason]

ok ya your right, on page 61. But WOW what a difference it draws between 4mhz and 20 mhz. If I go with 4mhz I would save alot even if I do only wake up once every 3 seconds or so.

The reason I'm useing this chip, well I dont need any options other than a voltage detector to determine when the power drops to 4.5v and I was using a voltage detector with a trigger at 4.5v. the chip I'm using cost $1.38 (the cheapest I found with 33 ios) here in mexico through newark. Do you know of other pics cheaper that are Flash ? I'm open to suggestions But I do preaty much have my board desgned.

[skimask]

ok ya your right, on page 61. But WOW what a difference it draws between 4mhz and 20 mhz. If I go with 4mhz I would save alot even if I do only wake up once every 3 seconds or so.

Power usage 'generally' goes up as the square of the operating speed...
i.e. 1mA @ 4Mhz, 4mA @ 8Mhz, 16mA @ 16Mhz, etc.etc...not always true, but generally.

The reason I'm useing this chip, well I dont need any options other than a voltage detector to determine when the power drops to 4.5v and I was using a voltage detector with a trigger at 4.5v. the chip I'm using cost $1.38 (the cheapest I found with 33 ios) here in mexico through newark. Do you know of other pics cheaper that are Flash ? I'm open to suggestions But I do preaty much have my board desgned.

If you've got the board designed and have it set up for an 'F59, then switch over to an 18F4620 (or even a 16F877). A bit more spendy, but loads more options, it'll plop right into the same socket with very few (if any) hardware changes, less current draw both in operation and standy with more options to run the clock, including clock switching in the middle of operation, and most importantly...interrupts that can wake up your PIC ONLY when a switch is tripped (see Interrupt on Pin Change in the datasheets for the above mentioned PICs), thereby meaning your PIC would be asleep EXCEPT when triggered by a door...which could mean that practically 99.9999999999% of the time, your PIC is sleeping. And I'd be willing to bet that the difference in price would more than make up for the new-found flexibility of the newer chips.

[jason]

Ya there alot more spendy. I'm trying to keep the cost down to minimal. here in Mexico in Newark the current chip is $1.38 and the 18F4620 is $7.28

However the PIC16F877A-I/PT is $5.70 and if I use a AD for the voltage detection which will save me about $2 that brings me down to $3.70, still a bit more. But like you say the added options. I will think about it.

[skimask]

Ya there alot more spendy. I'm trying to keep the cost down to minimal. here in Mexico in Newark the current chip is $1.38 and the 18F4620 is $7.28. However the PIC16F877A-I/PT is $5.70 and if I use a AD for the voltage detection which will save me about $2 that brings me down to $3.70, still a bit more. But like you say the added options. I will think about it.

One other thing to note...
The PIC16F59 is a 12-bit device, not a 14-bit device like the F877, or 16-bit like the 18F4620.
Using PBP, you'll be limited as to which commands you can use with the 16F59.
Maybe check out the 18F4410/18F4510. Looks to me like they might be a bit cheaper than the 16F877A.