Thankyou Elec_Mech, one more question I have, may be I should have asked this before all R&D, will the below one be easy than the one we discussed earlier,

1. A count down timer with screen where we can set count down like a digital clock.
(any thing like 8, 12, 24hrs countdown which displays on screen)
2. when the screen time becomes zero, it again starts countdown as setting and it starts our motor for set seconds

benefit in this is, user can set their custom time
but I'm worried about the screen cost, what is the cheapest available screen in market?
how much this module can cost than our earlier setup?

 

Hi PicoKit,
Thanks for your post, I hope you have gone through the requirements of this project.
Not sure how can I make use of your kit in my project, seems very different.

 

1. A count down timer with screen where we can set count down like a digital clock.

How many digits do you want? Just two for hours, e.g., 00-24? Or do you want four digits to count down minutes as well, e.g., HH:MM? The latter would require more parts and resources of course.

Are you only interested in displaying the count down duration or do you also want to display the motor run time?

To keep things simple, we'll assume you only want to display the countdown time with two digits to represent hours. We'll also assume the digits will be small, i.e., less than one inch (25mm) in height.

There are a number of ways to do this, each with pros and cons. I'll list a few here - someone else may suggest a more elegant or cost-effective solution.

• Use a larger PICAXE with more I/O pins, you could use a BCD-to-seven-segment IC such as a CD4543. You'd need eight I/O pins, four for each digit. You just change the state of the pins once an hour. The digits should be inexpensive, say $1 USD or less each. The ICs will be similarly inexpensive.
• Use a dedicated 7-segment driver IC such as the MAX7219. This can control up to 8 digits and only requires two pins from the PICAXE - the same two pins used for the DS1307 (connected in parallel). The caveat here is the MAX7219 will be expensive, about $13 in small quantities.
• Use a simple I/O expander to connect to the digits and control. An MCP23017 has 16 I/O's and can be connected to the same pins as the DS1307. This would allow simple control of two digits. These IC's are about $2 USD or less.
• Use a 2x16 character I2C-controlled LCD. Also expensive (relative to other options) at about $15-20 USD, but then you can display messages and show as many digits as you want. You could show both the countdown time as well as the motor run time at the same time.

The I/O expander is probably your most cost-effective solution. It does not require more pins from the last schematic I posted and you can add more than one of these to get more digits if needed - one IC will control two digits. To give a rough idea, this adds about $4 USD to the total cost for two digits ($8 for four digits, etc.). This is the cost for making a couple of prototypes - if you move to production, cost will drop as you will buy parts in large quantities.

There are a number of ways to control a display directly from a microcontroller, but they require more pins and speed than a PICAXE may be able to provide, so I have not mentioned them here.

2. when the screen time becomes zero, it again starts countdown as setting and it starts our motor for set seconds

So you want the countdown to immediately reset after the countdown reaches zero, not wait until after the motor runs? Easy enough to do in the software.