aarg:
1uA is definitely wrong. Was the display module illuminated? Some multimeters require that you plug the probe into a different jack for current readings.
Yes the modules was illuminted - See pics.
Here is a link to my UNI-T 30C multimeter.
Red lead was plugged into middle socket and connected to Uno 3.3V.
Black lead was plugged into COM and connected to the LED Module VCC.
Setting used was 2000 uA and reading was "- 001".
The 1uA would be for 4 segments.
Why do u think the reading is wrong?
What do believe the reading should be?
I would hate to think it is my meter - I only bought it 2 weeks ago.
Edited:
As an afterthought, I also measured 2 segments lit i.e. "1 1 1 1" and 7 segments lit "8 8 8 8".
In both cases I still get a reading of "- 001".
Wondering if that means my meter is not granular enough.
I did some test measurements this morning, and did some more research. I am fully able to justify my belief that this module is operating within safe parameters based on specifications and sound engineering principles, but I'm not willing to get dragged into a debate about it at this time. However I would like some confirmation of the peak current to be 100% sure. The design is not a good one, not mainly because it pushes the hardware to near its limits, but for the alternate reason of the segment dimming phenomenon that is due to lack of digit drivers. From a design point of view, adding those drivers would decrease the driving resistance and thus segment resistors would become more important. The real cost of four SMT transistors and 12 resistors is miniscule, a few pennies. So it's kind of stupid that they didn't use them.
Well it would seem according to my meter that the peak current would be 2 uA for four segments.
Although the reading mainly sits on one, it regularly flashes up to 2 briefly.
It does seem a lot of trouble to use, considering that the cost of modules based on chips like the TM1638 and others, is little more than the 74HCxxx drive ones such as yours. Although they also use a clocked serial interface, they have the strong advantage of managing all the scanning and LED drive on chip. Thus the Arduino doesn't have to continually update the display if it's not changing. As a bonus, the TM1638 can read switches (mine has 8 pushbuttons). It even has commands to change the brightness. Since the chip has proper scanning and drivers, the brightness is excellent.
I bought this module not knowing any better. I initially bought some 7 segment displays, but to my horror discovered they needed a lot of pins to drive. I was about to add level shifting to the displays, when I discovered there were some premade ones. So I ordered one to save myself the hassle of making one. But alas, I paid no mind to any technical issues - lesson learned.
Can u please provide a link to the ones u are using.
Bottom line is, to make your module's display really look good you have to change the software. I am willing to help with that if you like, but I doubt that it's worth it. The idea would be to illuminate one segment at a time as I outlined in a previous post.
This module was bought for the sole purpose of having the convenience of visualising the distances sensed by a sonar sensor during testing - so I don't really care about the brightness.
Bottomline:
I try to avoid controversy so would normally not comment, but since I feel a certain level of responsibility for raising the initial questions....
This post started out as a programming question. Aarg helped me resolve a programming issue for which I am grateful and thank him.
I threw in a few other questions and he was kind enough to respond to those as well.
Some may believe he did not give good advice, but the bottom line is I have to take responsibility for buying the unit and if it burns out ce la vie. The data sheet does not show the need for any resistors, so if blame needs to be laid, it should be at the feet of the manufacturer.
I am certainly interested to learn more about the technical aspects/limitations of the unit, but would rather it be discussed objectively and not at the expense of the reputation of someone trying to be helpful - after all we are only talking about a $1 piece of equipment.
That being said, I DO appreciate all the input, including constructive criticism, and thank everyone for their contribution.
