The 7490 counter is a negative edge triggered decade counter that counts from 0 to 9. Pins CLKB & QA must be connected for this counter in order that it would operate in the decade mode. The inputs R0(1, 2) & R9(1, 2) are asynchronous reset pins, one of each must be low for counting, if both the R9(1, 2) inputs were high, then the counter will be res
Click here to download the full size of the above Circuit.
et to 9, while if both the R0(1, 2) inputs were high while one of the R9(1, 2) inputs was low, then the counter will be reset to 0. Since the number indicating the minutes or seconds consists of 2 digits, then 2 counters are used, the one on the right counts from 0 to 9, while the one on the left counts from 0 to 5. For the counter on the right, the bit QD goes from HI (ie: 1) to LO (ie: 0) only in one condition, that is when the count goes from 9 to 0 (ie. from 1001 to 0000 in binary), so, it is used to trigger the counter which is on the left, so whenever the count goes from 9 to 0 at the counter on the right, the counter on the left will be triggered and incremented by 1, till the count becomes 6. For the counter on the left, the outputs QB & QC are connected to the R0(1, 2) inputs, so when the count becomes 6, the counter will be immediately reset to 0. Hence this stage will count from 00 from 59. Since the output QC for the counter on the left goes from HI to LO only when it is reset from 6 to 0 (ie. 0110 to 0000 in binary), so, it is used to trigger the counter in the next stage. The seconds stage is triggered by a 1 Hz astable multivibrator stage, the minutes stage is triggered by the QC output of the seconds stage (which is labelled "out CLK pulse" in the figure), and the hours stage is triggered by the QC output of the minutes stage. Since the maximum hour is 12, then the first digit is either 0 or 1, therefore...
This project fits more for custom made battery casing that can have more space to hide things inside. This switch with few alterations can be used for any other project as well but is designed based on e-bike needs! This project use a clever functionality of....
The circuit described here uses ultrasonic oscillations and operates based on the propagation velocity of these oscillations in the air. Thus, we can easily determine the distance of two points if the time within which the wave travels this distance is....
Sometimes the precious metals are hidden too deep and are not detected except with complicated devices. In many cases, however, small pieces of precious metal buried near the surface can be detected by relatively simple means. Everyone is very attractive to....
Many times for various reasons we forget or can not water the plants that we have in our homes. And many humidity sensors units just notify us with a beeping sound or with a flashing light, that the pot needs watering. But what if we are away from home? This....
The principle behind a metal detector is really very simple. Proof of this is the circuit that follows, in which it proves that the construction of a metal detector can be done in the minute, with few components that we find very easily everywhere. With the....
The sub-harmonic bass generator is a sound producing unit for guitars. The sound it produces looks very much like that of the bass guitar. The octave generator is sometimes quite unusual since it does not produce any of the usual ways of coloring the sound,....
In the past the sounding (sea bottom measurement) was done with the "bullet", that is, with a heavy lead object that the seamen plucked into the sea hung from a calibrated rope. As soon as the "bullet" reached the bottom, the depth appeared directly from the....
This Amplifier was designed to have the following specifications: Distortion less than 0.1% at full power of 100W even at 20KHz. Power has to be attributed to an extended bandwidth. The output transistors must be protected against short circuits. The power....
A series of LEDs serve to alert the gardener when plants need water. Using two conventional digital integrated LEDs and a series of LEDs, we make a very useful device for gardening. The device detects the amount of water in the pot and alerts the grower.....
characters left: