![]() The enhancement consists of modulating the signal produced by the “one-shot” timer, leading to a series of pulses with increasing (or decreasing) width.Just replace the three 1uf capacitors with 10nf capacitors (100 times faster!). The same circuit as the one in the simple version can be used to drive the shift register’s data input (this can be a good test to see if the circuit works fine up to this point). This extra signal is produced by a 74163 4-bit counter. One pulse every 16 is produced to drive the clock of the output register. “PWM-like” version: Here, the shift register’s clock works much faster than the simple version.(Schematic in figure 2, timing in figure 3) The second one works as a “one-shot” that is trigger by the former, so the user can control the length of the pulse. In order to have a good control of the “on” time, I decided to produce this signal using two (2) 555 circuits: the first one works as a multivibrator where the user controls its frequency. The “on” time of this signal determines the length of the drop. It has to have a frequency slightly greater than 16-times the frequency of the clock signal (the grater the difference, the faster the drop falls). Another timing circuit generates the shift register’s input data. ![]() Note that the 74HC595 has the shift register plus an output storage register: when both registers are driven by the same clock signal, the output is delayed by one clock period. Simple version: A timing circuit (555 as a multivibrator) generates a square pulse that drives the clock inputs of the 74HC595.There are two version of the circuit: a simple one and a “PWM-like”. ![]()
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