need help with a 8051 mcu project

Thread Starter


Joined Jan 16, 2007
hi everybodu im an student at colleage and i have to do a project from my first year with an 8051 microproccesor or any from this mcu family
i was given this circuit of an combination lock with a pic mcu but i have to use a 8051
this is the circuit

if any one can help me with this it will be great!


Joined Apr 20, 2004

There are quite a number of 8051 clones out there. Your concern is just with the electrical equivalent of the micro used in the example. Try a look at this site - - and see if you can't find what you need. My guess is that the 8051 clone by AVR will be easiest to use.


Joined Feb 24, 2006
"Danger Will Robinson"

I believe that elements of this design rely on the particular electrical characteristics of the PIC pin structure. You should be aware that the 8051 has what are called quasi-bidirectioanl outputs. They can sink a couple of milliamps when they are low but can source only tens of microamps when high. If you do not understand this point your efforts will founder on the rocks of despair.


Joined Aug 22, 2006
From your schematics, it is impossible to adapt to 8051. You should choose the chip i.e, Atmel, NXP, and then read its manual. Good luck. :)


Joined Feb 24, 2006
ok tnx guys i think ill use 89c52 now just need to write the program
The port pins on the 89C52 have the same problem as any member of the 8051 family. The port pins are COMPLETELY unable to create a logic high to provide base current for a transistor. If you copy this design onto an 89C52 you will have one awful time getting things to work.


Joined Feb 24, 2006
Use 2N7000's instead of the transistors.Simple.
It's only simple if you understand the operation of a 2N7000. Since there was an air of cluelessness about the port pin structure of the 8051 do you really suppose that he can modify this design with any hope of success? When things don't work will there be any basis for determining the cause?


Joined Mar 7, 2007
The circuit can be easily replaced with a 8051 derivatives such as the Atmetl AT89S52, AT89S4051, etc. I would normally use a darlington paired transistor such as the MPSA14 to reduce the base current requirement instead of single ended npn transistor.

The AT89S52 can be programmed simply using this software provided by some smart chap at .

You can get a free compiler at . I have tried this. Very good, though Keil compiler is still my favourite.