Binary clock


Joined Jul 17, 2007
The bridge rectifier is not connected properly.
D3 (bridge rectifier) should be connected as:
1 -> +V out
2 -> T1 pin 2
3 -> T1 pin 3
4 -> Ground
Another mod to the clock input... :rolleyes:
Disconnect D5, connect R21 directly to the input of U17A.
Re-connect D5 with the cathode to +5V, anode to the input of U17A.
This way, the input to U17A won't exceed Vdd + the voltage drop of the diode (around 0.7v)
An arguably better solution would be to connect a 4.7V Zener diode from the input of U17A to ground.
The input wave won't go negative more than 0.7v due to the bridge rectifier connection to ground.

Thread Starter


Joined Jun 25, 2007
Argg, I hate the diode bridge, Wiki has it rotated one way and i have it another way.

I think that a 4.7 zener would work better.
Also you asked where I got the photo transistor circuit from, well I made it up, first I used a pot then replaced it with a photo transistor, Will it work to dim the leds?

Ok I have changed that. I did not really get what you meant with the resister. Does the resister connect to the input and the diode on the other end?


Joined Jul 17, 2007
Yes, you have Zener D5 and R21 hooked up correctly now, along with D3 :)
Resistor R21 limits current flow through Zener D5, which prevents the input to the Schmitt-input inverter from exceeding 4.7V. The maximum current flow through Zener D5 will be determined by what the secondary voltage of your transformer is, but it shouldn't exceed more than a couple of mA at the worst.

The easiest way to think of a diode bridge is that the diodes point away from the most negative potential, and that the AC input has to have a two-way street. Or in other words, "Point towards positive, AC two ways". Memorizing such short phrases can help a great deal in remembering what goes where. ;)

U13 and associated is going to take a bit of work yet. A 7805 won't be appropriate, as the MINIMUM output will be 5V. You can INCREASE the voltage output, but in order to DECREASE the voltage output, you would need to have a negative voltage reference - but there are no provisions in your circuit for a negative reference, and that would unnecessarily complicate things. Let's re-visit this topic later.

Let me think abouthe clock setting circuit for a few.


Joined Jul 17, 2007
Here's another phrase that will help you to remember resistor color codes (sanitized for a G-rated forum):

Bad Boys Ravish Our Young Girls Behind Victory Garden Walls
It makes more sense when put vertically:
Bad = Blk = 0
Boys = Brn = 1
Ravish = Red = 2
Our = Orn = 3
Young = Yel = 4
Girls = Grn = 5
Behind = Blu = 6
Victory = Vio = 7
Garden = Gry = 8
Walls = Wht = 9
So, if you can remember that phrase that I learned back in the 70's, you two will be quickly able to decipher the meaning behind the stripes on resistors ;)