Hi all.. New issue... I have been using the adafruit 4 segment 1.2" led displays for a while now. Have used the red, yellow and the green ones. they all work ok,,
A friend asked if i could make her a clock using a blue display.. It wasn't easy to find, but i finally found some 1.2" Blue led displays.. they fit the backpack board perfectly, the backpack uses the HT16K33 led driver chip.
This is the Display data sheet .. The seller assures me that the display operates within the 5v range.. When i connected up the display, only the dots light up.. None of the digits.. what am i missing here ??
it's not really a matter of them.. I have working displays and the same backpacks with the different colors i mentioned.. I'm just wondering why the display does not function.. I included the schematic of the display. I'm try find out if the outputs are not at 5v... or if they are lower, or if china lied to me about the displays..
My other displays are working with a GPS clock i made.. so i thought a color swap would swap right over. apparently not..
Maybe try a voltage and resistor chasing the pinout to prove it is what it claims to be…
Remember that blue LEDs typically require a higher voltage.
If you’re confident in everything else, the supplier must have dudded you, we can’t help.
If you have added the BLUE display yourself to the HT16K33, have you compensated for the increase volt drop across the LEDS and hence lower current flowing thorough them?
Are you sure the display is pin for pin the same as the red etc, are they from the same product series you post the data to?
The data sheet is misleading. The forward voltage shown in the table is for each led, but the segments contain 2 LEDs each, so the forward voltage of the segments is 5.6~6.0V:
I did some flat testing today.. the display is nice and bright at 5.4v very dim but visible at 5.1v
I'm wondering now also.. if the hi speed strobing of the driver further makes the display dimmer to where it's not visible .
From the datasheet: https://www.digikey.com/htmldatasheets/production/2070902/0/0/1/ht16k33.html you can see that the absolute maximum voltage you can drive the HT16K33 at is 6.5 volts. You could drop the voltage to the rest of the circuit in units of 0.7 volts by using normal (silicon) diodes in series, if required.
I can't see that the screen scanning pattern has much of an effect on the brightness but there may be some switching losses. The sharp cutoff in brightness you've seen is due to the forward voltage of the leds (already mentioned)
Exactly. You probably don't want 2 separate power sources for your clock. If, for instance, you used a 6 volt power supply, which may be good for the display, that may be too much for some other components.
In your case, if it is only a Nano and a GPS module, then both will have internal voltage regulators and so 6 volts or so will not be a problem. If, however, you were using a raw ATmega328P you could not use 6 volts to power it and would then need to reduce the voltage somehow. Hence the suggestion of the diode(s) as voltage droppers.
Another possibility is to power the Nano, say through its USB interface with a phone charger, and use small boost converter to get the 5.4v plus required for the display module.
