strokedmaro
New Member
Well, I come to the electro gods again for help... What seemed so simple (in theory) operates completely unexpectedly. Attached is the datasheet for my problem child...the MC4028BE BCD to decimal decoder.
SETUP: Vdd=12vdc, Vss=ground, input "D"=grounded, Inputs A,B,C are attached to pushbuttons to 12vdc.
With no inputs I get 6vdc on (pin 3)...shouldn't it be closer to 12vdc?
With inputs on A, B, and C (pin 4) reads 12vdc but I also noticed it stays at 6vdc when inputs removed...so It jumps only 6vdc when activated.
All other outputs start at 0vdc and go to 6vdc or so.
I would think they all start at 0vdc and output Vdd when activated but that is not whats happening obviously. This happens with 3 exact chips...I've also set it up several times on the breadboard to make sure I didn't mess the wiring up.
Ive also attached a pic of exactly what I have on the breadboard. Keep in mind that pin 4 always has 6vdc on it so the LED dims immediately. when pin 4 is active the 12vdc is enough to kill the LED completely....when 15 is active the led goes out completely but only outputs 6vdc. I think the 6vdc from pin 4 plus the 6vdc from pin 15 together make this happen because no other output will extinguish the LED including pin 15 if pin 4 is not connected. HELP HELP HELP!!!
Any help appreciated!!!
SETUP: Vdd=12vdc, Vss=ground, input "D"=grounded, Inputs A,B,C are attached to pushbuttons to 12vdc.
With no inputs I get 6vdc on (pin 3)...shouldn't it be closer to 12vdc?
With inputs on A, B, and C (pin 4) reads 12vdc but I also noticed it stays at 6vdc when inputs removed...so It jumps only 6vdc when activated.
All other outputs start at 0vdc and go to 6vdc or so.
I would think they all start at 0vdc and output Vdd when activated but that is not whats happening obviously. This happens with 3 exact chips...I've also set it up several times on the breadboard to make sure I didn't mess the wiring up.
Ive also attached a pic of exactly what I have on the breadboard. Keep in mind that pin 4 always has 6vdc on it so the LED dims immediately. when pin 4 is active the 12vdc is enough to kill the LED completely....when 15 is active the led goes out completely but only outputs 6vdc. I think the 6vdc from pin 4 plus the 6vdc from pin 15 together make this happen because no other output will extinguish the LED including pin 15 if pin 4 is not connected. HELP HELP HELP!!!
Any help appreciated!!!