i got problem on designing this digital dice, we were told to use "combinational circuits", but i dont know how. i saw some circuits which use 555 timer and 4017 counter, but are these ICs for combinational circuit(opposite of sequential circuit)? and even though they are allowed, how do they function? can anybody help please? tnx!

 

I think I saw that project once, but I cannot do anything without a circuit. Post the link to the page, if you please.

 

http://www.electronicsforu.com/electronicsforu/lab/ad.asp?url=/EFYLinux/circuit/oct2005/CI-02_Oct05.pdf&title=Digital%20Dice

http://www.kpsec.freeuk.com/projects/dice.htm

http://www.talkingelectronics.com/projects/LED-Dice/LED-Dice.html


i like the first one because it uses logic gates outside the ICs, but i dont know what the gates do because i dont know the inputs to the gates which are the outputs from the 4017 counter.

 

Basically, the 555 is in astable mode and provides pulses to the 4017 counter. The counter "counts" the pulses, changing its output each time it receives a pulse, in the sequence:
Q0 1 2 3 4 5 6 7 8 9
1 0 0 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 0 0
...and so on.

In the second project, the logical combinations required to light the LEDs are made using diodes. The Q6 is used to reset and go back directly to Q0. Instead of using diodes, you can use gates to light up the LEDs. The second project is the best, since the touch plate should be avoided. You should stick to TTL or CMOS only (the CMOS family can drive well LEDs and you can use a 9V battery to power them directly). Using the 555 timer to activate the 4017 chip is bad practice. You should go to the CMOS version, the LMC555.