Random seed using the ds1307 RTC

Hi, first time poster, long time lurker.

How best can I use my ds1307 RTC to set a unique seed for use with RANDOM.

I know that the RANDOM seed needs a 4-byte value, and to the best of my knowledge the DS1307 only returns, seconds, minutes, hours, day, month, year, day of week, and not microseconds.

I want to randomize this as best as I can taking advantage of the RTC.

Anyone have any advice?

Thanks

Can't call it advice, more like an idea.

When powering up, start a 16-bit timer and let it free run until you get a transition from the 1307's SQW pin.
Should give a halfways decent seed.

You'll have to turn on the Square wave output on the 1307 first.
AND, you need to make sure the seed is never ZERO.
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Random requires (required) a non-zero WORD variable as a seed... I haven't checked if this has changed with v2.50...

If that's the case just multiply all the DS1307's CLOCK registers together 'as-is' into a WORD variable without even bothering to convert from BCD. You'll spill out of 16-bits, but it won't matter - PICBASIC just keeps on trucking ignoring the spillage. If the end result is zero then either just add 1, or repeat the itteration.

What I want to do is generate a random number between, say, 10 and 30. But from what I did, the numbers progressively get larger in sequence and do not look that random. If the seed is larger, does that mean that the random number generated will be larger? Also, I noticed that the random number generated goes above my max limit.

Here is my simplified code below with the output following it. How can I improve my code to get a more random looking output? Note that this device won't power cycle that often, so I don't want to rely on the reading/writing to the eeprom on start that much, but I did include it in my code to add an eeprom value to the seed.

Code:

---

RandomSeed Var WORD
RandVal  VAR Byte
Cnt2  VAR Byte
MinCnt  VAR Byte
MaxCnt VAR Byte
Cnt2 VAR Byte

MinCnt = 10
MaxCnt = 30

Read 0, Cnt2
Write 0, Cnt2 + 7

i2cread SDApin,SCLpin,$D0,$00,[Seconds,Minutes,hours,dow,day,month,year]

Randomseed = (Hours+1) * (Minutes+7) * (Seconds+3) + Cnt2
Random RandomSeed
RandVal= (RandomSeed//MaxCnt)+MinCnt

Debug dec2 RandVal,CR,LF

---

Output:

Code:

---

10
10
12
12
14
14
28
28
30
33
33
35
35
36
36
38
38
11
11
13
13
15
15
17
17
31
31
33
33
34
34
36
39
39

---

Thanks for any help.

Can anyone provide some guidance with those 2 issues I'm having? (number generated is out of my range, and number generated always increasing)

Maybe this might work ...

A random number is always a word variable.
The value is always between 1-65535.

So if the 1-65535 is considered the Decimal part, then multiplying it times the range you want (in your case 20) and take the High Word result, then add the minimum...

Code:

---

Value  VAR WORD
RND    VAR WORD
MinCnt CON 10
MaxCnt CON 30
Scale  CON MaxCnt - MinCnt

RND = 1234 ; The Seed, however you get it

RANDOM  RND
Value = (RND ** Scale) +  MinCnt

---

Base on Darrel code, this line >>> Scale CON MaxCnt - MinCnt << should be Scale CON MaxCnt - MinCnt +1, so the maximum range will be reached.

Thanks Darrel.

I also attached a little file making a set of 6 random numbers range from 10 to 30 based on Darrel code.

Someone's paying attention!

Yup you're right KVLV.

+ 1
Why do I always forget that part?

Thanks for the example too.
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