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The mistake was corrected by cutting the ground connection datzsheet conecting the respective pin to the enable singal itself which was available from the pin right next to it.

Like in the solar charger designa 74HC quad tri-state buffer is used together with some resistors and capacitors. There are various contrast settings that must be set properly via I2C commands but there is very little datasheeg on those commands in the data sheet. The backlight brightness is controlled by the other digipot via an op-amp and a n-channel mosfet. When the enable signal is high, the display is on, when enable is low, the user interface dtasheet into its low-power state.

74hc126 datasheet pdf

As a result, the display as well as all the other components only get to see about 2. With rotary encoders things get much trickier.

Ultra Low Power State Another design requirement was to keep this a very low-power design. I mean CMOS is close to zero-power when static and only a single tri-state gate is active so essentially no current flows.

Power consumption Very low standby power consumption was one of the key design goals. And as mentioned, the op-amp was not a great choice for the job at hand. As long as the push button is not pressed, no power flows there so the only power consuming device is the 74HC I asserted the enable signal and nothing happened.


M54/74HC datasheet & applicatoin notes – Datasheet Archive

So the measurement works and it seems that the 8 microamps given in the data sheet are just a very conservative worst case. And a time constant of a few milliseconds is totally sufficient so you might end up with something like 10ms of delay.

One then needs to wait for 5ms before the initialization sequence is sent. So there will be a Rev B of this board with those issues solved. The basic circuit is exactly the same but choosing the right component values is more difficult. Add a dual I2C digipot to control both the reset signal as well as the backlight. The logic is pretty datasheeet the same here except that I use different non-inverting gates here.

Nor the timing of the reset singnal.

74HC | soldernerd

The reason for that is the need for 3-state outputs as mentioned before. 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. If you use a time constant of a few milliseconds like with the push button you will not be able to detect when the encoder is turned quickly. Power can now always stay datashedt. After the two hardware fixes this user interface works quite as intended. 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 datashet the push button still works in order to wake up the microcontroller.


Toghether with the positive feedback via the k resistors that works very well. My final solution was as follows: Testing First of all nothing worked at all. Nothing was powered on. On the positive side the debouncing works just perfect with the chosen component values.

I expected to tweak those values a bit but found that they work so well that I just leave them as they are. The reset signal needs to be pulled low for 10ms.

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. First of all nothing worked at all.

Tag Archives: 74HC126

Since there are 4 gates on the 74HC and I only need to debounce 3 signals, there is still one gate left. Then ok, power was there but when I tried to turn off the ddatasheet singal i. When in low-power mode only the push button pull-up and the 74HC is supplied with power.