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I figure since the latter was normally used in older computer systems, the power supply and input signals are expected to be well-filtered and free of noise.
When the capacitor stops charging up, the 22K pull-down resistor pulls the clock input down to a logic 0. Assembly and Dxtasheet Completed 744ls393 of assembly bottom view Back to Top. Most chips come with four AND gates in one, or 6 inverters in one. So, when the hours runs to 13, the AND gate will reset the hours to zero, then the DRL will produce a logic 1 because it senses 00 hours.
I designed the clock circuitury hoping to dstasheet a perfect design that uses all of the logic available in all of the chips I would need. I had to use a very small 8-volt transformer that just barely fits inside the case to supply the low voltage power.
In the process of constructing the clock, I found that these chips were extremely sensitive to noise. As a result, when the clock is turned on, the 1 is always on. None of the other digits have this trait. I found a “trait” of the 7-segment zero digit, segment F has to be on and segment G has to be off. I figured that with the in the front, it would buffer out more of the noise and generate a cleaner clock pulse for the 74LS chips.
The and triggers on the rising-edge. I planned on placing the neon bulbs under each digit, so if you’re plain then look at the Bs and if you’re a geek then look at the binary below. I used the for the first stage to divide 60Hz to 10Hz. I originally planned on using a Mostek MK 6-digit clock chip that multiplexes the digits.
I realized a design flaw when I finished the clock.
For this clock, I decided to go with the traditional 7-segment display to show the time. The fundamentals of my binary clock circuitry was based on Hans Summer’s binary clock, but his operates in hour mode. Recall that the 74LSs trigger on a falling edge, not a rising edge.
I figured that if the clock was going to roll over to 00 hours, I’d need a “double” pulse to get the hours to automatically advance to 01 hours. I built a case out of cedar, and the amount of space I had inside the case was rather limited so I was unable to pursue my idea of using neon bulbs or LEDs for displaying the binary time directly from the 74LS counters.
The datasheet says the chip was designed to have a strong tolerance for noise, and there is no mention of this in the 74LS datasheet. When the clock goes to 10, 11, or 12, the “C” is turned off so the digit 1 appears. However, that didn’t work out due to complications with the circuitury and the amount of room in the clock case I made.
There, you have it, a “double” pulse to get rid of the 00 hours. The “C” that is switched on to make a zero comes on when the clock is in the single digit hours.
Motorola 74LS Series Datasheets. SN74LS, SN54LS, 74LS Datasheet.
Without the K resistor and 0. A colon indicator can be added by using the 1Hz pulse off pin 5 of U3a. I came to a point where I thought I had gotten the design, so I proceed to build the clock.
I was faced with the problem of the clock starting at 00 hours, but the clock does count nicely to 12 and resets back to However, I had to delay the pulse from the DRL until the 10 minutes counter finished sending its clock pulse to the 1 hours counter. It took some experimentation before I could get the signals to work correctly between the chips. Even a seconds display can be added to this circuit, simply add two more decoder chips on U3b and U4a. For the ten hours, I didn’t want to waste another 74LS and chip just to display zero and one.
I think if the 74LS operated on a rising edge, the circuit might work without the capacitor and resistor. As you can see in the schematic, the portion marked in blue uses two AND gates and one inverter gate. This falling edge triggers the 74LS to advance one more time. I never had a problem with this in my other two clocks that run off mains, and I discovered the reason after taking a closer look at the datasheets.
The other segments for the zero are all wired together and switched on and off by a flip-flop.
The inverter using a transistor and resistor changes the “off” G into a logic 1 for the AND gate. I daatasheet found out that the circuitry draws a good amount of current so I couldn’t simply obtain low voltage from the voltage doubler and regulate it for the low voltage supply like I could in my first two nixie clocks.
I tossed this idea out and decided to drive the nixies directly, using BCD-to-7segment decoder chips. Therefore, both diodes have to have a logic 1 in order to allow the output to rise to a logic 1. This would’ve been a bad waste of chips, so I decided to do the remaining logics the 74ls3933 school way This configuration helped solve the problem. Below is the pinout of the B nixie: So much for the “perfect” design that used all of the chips wisely.
The 74LS clock input triggers on a falling-edge of a square wave when the square wave signal drops from a logic 1 to 0. Click here for the schematic diagram of the four B nixie clock.
74ls datasheet pdf
These versatile nixie tubes can allow for a variety of characters and digits with different styles. One advantage to use what is essentially a binary clock with 7-segment decoders is to have small neon bulbs or LEDs driven directly from the BCD outputs.
This current draw will pull up the clock input of the 74LS to a logic 1 momentarily.