74HC Buffers & Line Drivers are available at Mouser Electronics. Mouser offers inventory, pricing, & datasheets for 74HC Buffers & Line Drivers. 74HC Datasheet, 74HC Quad Buffer/Line Driver Datasheet, buy 74HC M54/74HC September QUAD BUS BUFFERS (3-STATE). B1R. ( Plastic Package). ORDER CODES: M54HCXXXF1R. M74HCXXXM1R.
|Published (Last):||3 September 2010|
|PDF File Size:||4.79 Mb|
|ePub File Size:||2.39 Mb|
|Price:||Free* [*Free Regsitration Required]|
The error was soon found. Just use a relatively long time constant i. The debouncing is basically unchanged. There is an older version in the net somewhere that mentions those timing issues and at least gives a sample initialization sequence. I also considered adding a sub-dollar PIC16 which could be programmed as an I2C slave and control both the backlight and the reset signal as well as giving the option of getting the encoder input via I2C.
Nor the timing of the reset singnal.
(PDF) 74HC126 Datasheet download
The reset signal needs to be pulled low for 10ms. That eliminates the need to design the same functionality think debouncing again and again. And it was not very elegant that the display was powered off by just cutting the entire power supply. Testing First of all nothing worked at all. As a result, the display as well as all the other components only get to see about 2.
Toghether with the positive feedback via the k resistors that works very well. Like in the solar charger designa 74HC quad tri-state buffer is used together with some resistors and capacitors. Not pretty see below but problem solved. I still need a way to control both the backight as well as the reset signal without needing any more singnals.
Actually the measurement fluctuated between about 0 and 15 nanoamps. Next steps After the two hardware fixes this user interface works quite as intended. Another design requirement was to keep this a very low-power design. The mistake was corrected by cutting the ground connection and conecting the respective pin to the enable singal itself which was available from the pin right next to it.
The backlight brightness is controlled by the other digipot via an op-amp and a n-channel mosfet. While the display got its own little board, the encoder connected directly with the solar charger where its signals aredebounced in hardware and then routed to the PIC. Since the display connects via I2C it was quite straight forward to use I2C communication for those purposes as well.
In that state the user datasyeet must not use more than a few microamps. Use the previous backlight PWM signal as an enable signal.
74HC | soldernerd
The latest version uses a 4 lines x 20 characters LCD that connects via I2C as well as a rotary encoder with a push button. As long as the push button is not pressed, no power flows there so the only power consuming device is the 74HC One then needs to wait for 5ms before the initialization sequence is sent.
On the schematic the wire touched the respective pin but there was no connection. After the two hardware fixes this user interface works quite as intended. When in low-power mode only the push button pull-up and the 74HC is supplied with power.
Even less pretty but problem solved anyway. But when the user interface is not in use, we need a way to put it in a very low power state where the display as well as the rotary encoder is off but the push button still works in order to wake up the microcontroller.
I asserted the enable signal and nothing happened. As so often, google was my friend and others have faced similar problems before so I managed to find some commands that make the display work properly.
Well, if you think so too, think again. Power can now always stay on. They make nice, pretty and affordable displays. That will introduce some delay in the output signal but as a rule of thumb anything below 50ms is not noticable. This was a bit harder to fix than the previous error. Another issue I noticed was that the LM op amp I had chosen is not a rail-to-rail op amp. So there will be a Rev B of this board with those issues solved.
Ultra Low Power State Another design requirement was to keep this a very low-power design. I then decided to design an new board that also includes the rotary encoder with all the necessary debouncing.
And the commands for this black-on-white display are different to the otherwise identical white-on-blue display. But with the hardware debouncing applied here we get a clean, digital output singal nevertheless. Using the spare gate to supply the rest of the circuit with power was not as good an idea than I thought.
SGS Thomson Microelectronics
My final solution was as follows: Since there are 4 gates on the 74HC and I only need to debounce 3 signals, there is still one gate left. When the enable signal is high, the display is on, when enable is low, the user interface goes into its low-power state. I mean CMOS is close to zero-power when static and only a single tri-state gate is active so essentially no current flows. The basic circuit is exactly the same but choosing the right component values is more difficult.
So the enable signal only controls the input of that gate. The LM is inexpensive and I had quite a few left from another project so I used it without giving it much thought. The entire initialization sequence needs to be written in one single I2C transmission.