The virtual Forum provides free access 25 on-demand webinars which have been recorded at electronica. In our simple example above, the input clock pulses are from a push button switch but counters can be used to count many real-world events such as counting moving objects. Clocked T-type flip-flops act as a binary divide-by-two counter and in asynchronous counters, the output of one counting stage provides the clock pulse for the next stage. Connect pin 2 to pin 9 and pin 3 to pin 8. Mabye manually applying a clock is causing problems.
Some inputs are 'active low' which means they perform their function when low. It is useful in a large number of counting applications in digital computer systems, data handling systems and control systems. Generally 7-segment displays require about 12 to 20 milli-amps to illuminate the segments, so the resistive value of the current limiting resistor all will be identical is chosen to limit the current to within these values. With inputs from 10 to 15 1010 to 1111 in binary all outputs are high. They are ideal for slowly changing or noisy signals. So for ten pulses in there is one pulse out of this pin.
The number of pulses counted up to 9 appears in binary form on four pins of the ic. The counter may be preset by placing the desired binary number on the inputs A-D and briefly making the preset input low. The decade counters count from 0 to 9 0000 to 1001 in binary. If you click on these the advertiser may know that you came from this site and I may be rewarded. I deliberately clocked them the way I have so that each frequency output is a symetrical square wave. But we can do this in two ways. When connected to logic 1, the Reset inputs R 1 and R 2 reset the counter back to zero, 0 0000 , and when the Set inputs S 1 and S 2 are connected to logic 1, they Set the counter to maximum, or 9 1001 regardless of the actual count number or position.
The inputs A-D may be left unconnected if not required. These parts are prefixed with 54 instead of 74 in the part number. For the 74162 and 74163 synchronous reset you must use the output s representing one less than the reset count you require, e. In a permanent circuit it is wise to connect any unused inputs to +Vs to ensure good immunity to noise. It counts the input pulses and the output is received as a 4-bit binary number through pins Q A, Q B, Q C and Q D.
Aah that makes a lot of sense now. Very interesting site btw, I'll be back to check out more. Note that the 7442 can be used as a 1-of-8 decoder if input D is held low. Please don't sent me private messages about electrical topics. The inputs A-D may be left unconnected if not required. One is used for the seconds and one is used for the minutes.
Not all functions are available in all families. It is suitable for easy interchange and addition. These are counters so beware that glitches may occur in any logic gate systems connected to their outputs due to the slight delay before the later counter outputs respond to a clock pulse. I knew of the negative edge trigger but I thought that it would be on the negative edge of a positive signal into the input. We saw previously that toggle T-type flip flops can be used as individual divide-by-two counters.
All chips in the following sections are available 4 to 12 pin. The original family now obsolete had no letters, eg 7400. . That is from 0 to 15 in decimal. They can up to about 20mA.
Thanks a million for your post, which was very clear I only had a 10 nF capacitor to hand, but I can't get the 7490 to produce a working output yet. Note that although it will be a 2-digit counter, values representing Hexadecimal numbers from A through F are not valid in this code. Note that the 7490 has a pair of reset9 inputs on pins 6 and 7, these reset the counter to nine 1001 so at least one of them must be low for counting to occur. The 4-bit counters count from 0 to 15 0000 to 1111 in binary. To count above 10 and produce a 2-digit base-ten counter and display, we would need to cascade two separate divide-by-ten counters together. Hi raiz Attached is an image from the 12 counter. They are counters so beware that glitches may occur in logic systems connected to their outputs due to the slight delay before the later outputs respond to a clock pulse.