for new project: random number generator with memory

[teletot]

I'm looking for information for a new project:
when pushed touch button, a lcd display should show a 8 digit random number for approx. 15 sec., in a memory function the generated numbers should be stored with date and time stamp and shown, on demand by scroll function, on display. Stand alone system on printboard, battery operated.

 

[MikeMl]

How many button pushes do you need to store?

 

[teletot]

min. 50 and max. 100 button pushes

 

[MikeMl]

Seems like you could do this with a battery backed-up ucontroller. With careful packing, each button push would generate about 8-10 bytes. With 2K bytes of ram, you could store >100 events... One with an SD card interface would not require battery-back-up and could store millions of events...

 

[BeerBelly]

A Microchip 24lc128 EPROM memory stores 16k by 8bits. It's easy to interface and costs 75 cents.
The first thing to do is determine which components will be needed.
Microcontroller,Display,Button,Memory?

 

[Mr RB]

How are you going to generate a perfect 8 decimal digit random number?

There are probably three easy methods;
1. generate a digit 0-9 for eight iterations
2. generate a number in exact range 0-99999999
3. generate a 27bit number (range 0-134217727) and discard result and re-run if over 99999999

 

[dougy83]

With careful packing, each button push would generate about 8-10 bytes.

A timestamp having a 1 second resolution over a 20 year span only requires 29.2 bits; 8 digit number only needs 26.6 bits. That's a total of 56 bits (7 bytes).

One with an SD card interface would not require battery-back-up and could store millions of events...

This project needs battery backup for the realtime clock (for the timestamps). The clock can be in the microcontroller or an external RTC IC.

 

[teletot]

Okay, where do I start and what components do I need to get this job done.

 

[dougy83]

If you're happy to use an ATMEL AVR device, then you'd need:
* ATMEGA48/88/168/328 (just one of these) Revision D or later (or the 32kHz TOSC is no good),
* a 32kHz crystal for the RTC,
* an HD44780 LCD (I'm assuming you're OK with one of the 2x16 character modules..???),
* a switch,
* some capacitors e.g. 2x 16pF, 1x 10uF, 2x 100nF,
* a programmer, e.g. USBISP or USBASP
* batteries and holder, and
* a programming connector (e.g. 2x5 or 2x6 DIL pin header).

This can be programmed easily using AVR-GCC or WinAVR C compilers.

Regarding saving the numbers and timestamps, the program memory can be used for this purpose; just note that blocks of 32 bytes should be written at a time (RAM or EEPROM can be used for short-term storage of this data).