EDIT: After short discussion and walking through ESP documentation, I decided to throw up PWM using OE pin (ESP does not have HW PWM), and use do it as part of multiplexing as Kartman suggested. Thanks
I'm doing very original project you never heard of - a clock. It will be my first use of PNP/NPN (especially the high-driver side) and shift registers, one reason to not use any led driver.
The project will be supplied by 9V, controlled by ESP8266 which will feed two 74HC595 by data. All transistors should be their SMD versions (bought as MMBT3904 and MMBT3906). The 7 segments display are some cheap chinese, common cathode, most probably with two red LEDs (their voltage drop is little bit below 4V).
The whole schematic would be pretty huge, so I'm pasting just the part I'm concerned about - driving one segment on one display. There will be two SR (shift registers), one (SR1) for driving actual segments and one (SR2) for driving low-side (common cathode) - basically for "selecting" a display to display number on.
And, I would like to add a special function - dimming, which I would like to achieve using PWM-ing an OE pin, which should change "Input from SR1" to open collector. In my head and on the paper, it works. However before I order the PCB and start endless soldering of few hundreds of pins, I would like to ask you, more experienced:
- Is it even a good idea?
- Will this design work at all?
- Does it have some major (or minor) flaws?
Thank you (and sorry for little bit lame question)
simulate this circuit – Schematic created using CircuitLab
