Need help with first project.

@inst-tech Hi Louis, First, thanks for continuing to help with this project. I just want to explain that I chose to use a common anode type LED only because at the time I was shopping for any available 3 inch digit size,(which is already limited), common anode types were all I could find. Now that I see your post with a possible solution, (thanks again), you mention that trying to use a common anode unit is limiting parts choices, possibly making my fabrication more difficult and preventing you from bench testing your idea. After reading your post I went back to the web and looked a little harder for a common cathode type, and now (embarrassingly) see that if I had beat the bushes a little more the first time, they are in fact out there. So, if you think it would help, I'm happy to purchase some of those, I need two, and I can also (somehow) send you one to allow for your testing. Please let me know when you get a chance. Bill

@billinfl, Hi...I'd hold off on buying any more parts until we can check the feasibility of those parts working for your design parameters. If you could please post the part# of those common cathode 7-seg displays you found, that would help alot in determining what drivers will/ or will not work. I haven't seen many 3" common cathode type, but if you've found some, that'd be great. Then when you get the display working..we can try interfacing it with your scale.. That should be to hard...lol

Looking forward to seeing your project to completion..

Regards,

LouisR

Hi Bill @billinfl,

   To back up what Louis @inst_tech is saying, I would say common anode LEDs are usually easier to drive than common cathode.

I have done some further experiments, and I am slowly 'writing them up', the slowness being partly due to some distractions over the last 3/4 days. However, I hope they will be helpful.

As a 'spoiler', I think the LEDs you have will be fine for your first prototype. You will need some extra parts (hopefully low cost), and I hope to describe some choices/possibilities, etc. in the near future, as well as some rough code to get started with, so you can begin to visualise the 'whole story'. Sorry it is taking me a little while.

Best wishes, Dave

@inst-tech OK. Got it. Thanks. Here's one common cathode I found, and some data about it, along with the part number (see pic) of the ones I already have "on hand". (Not sure if photos worked).

@inst-tech Crap. C

an't figure out how to post more than one at a time.

@inst-tech

@davee Thanks Dave, all sounds good. No need to apologize about delay. I'm not in a hurry, and this project has no "drop dead date". I much appreciate the help I'm getting from you and others on this board, and will sit tight as you brainstorm. Now, I'll return to learning how to (properly) post photos.lol. Bill

Hi Bill @billinfl,

  Photos worked fine. I sometimes have photos etc. as files on my PC, and then use Attach Files, rather than drag and drop. I don't why, maybe my ignorance or PC setup, but drag and drop sometimes seems reluctant to play nicely, whilst Attach Files seems more reliable.

Best wishes, Dave

PS I see you posted to me whilst I was typing this note. Thanks for the kind reply. Perhaps you will be able to share the secrets of direct posting of photos on 'bad' days, when you discover them. Some days, it seems easy ... others not so easy!

@davee I'm a Mac user and I almost never use Drag'n'Drop. I think I used it more on my Windows machine LOL. Much faster and easier to use Cmd-C and Cmd-V.

Hi Ron @zander,

 Thanks for your contribution. I too, use CTRL-C, etc. depending on what is most convenient at the time. Unfortunately, I have found this forum also shows the same issue with Ctrl-V, when posting pictures. It doesn't happen all the time, just when it decides not to play nicely ... perhaps it doesn't like my sermons ... !

Best wishes, Dave

@davee I don't often use Copy/Paste to put pictures on the forum, but a few days ago I did something like that and it disappeared. It was a larger than normal file for me but I don't think it was that big. 

No comment re the sermons 'accidently' messing up.

@billinfl To post multiple pics, click the 'Attach Files' at the bottom of the post window. See pic.

If you posted a pic or some other file in the past and want to attach it to another post, use the My Media.

@davee , @billinfl, @zander... Ok, I think I may have found a viable solution to the problem of how to drive high voltage common anode 7 segment displays.. A solution could be using a TLC5916 display driver.. shown pictorially below:

 This chip uses constant current source and only requires one resistor! While it's similar to what I did with the Sn74HC595 in a previous post, it can use higher output voltage because it's constant current.. @davee, take a look at the data sheet : https://www.ti.com/lit/ds/symlink/tlc5916.pdf , let me know what you think..

regards,

LouisR

Hi Louis @inst-tech and  Bill @billinfl,

  Thanks Louis for another great suggestion ... so far I have only had a glance at the data sheet. As always, TI have done a pretty thorough job on the sheet, and I think it would be a great choice for a 'professional' product.  My only concern is that it maybe a bit scary for a newcomer, as it packs quite a lot of tricks into a small box. So I hope you will not be upset if I also continue to suggest a simpler device like the ULN2003, at least as an 'icebreaker' to smarter things in the future. I encourage all readers, including Bill (@billinfl), to consider the best course of action for their personal project.

------------

I have finally managed to post my experimental mock up on the forum regarding this whole question. As (no surprise), it is rather long, so I have created a new thread for it to hide in, at:

https://forum.dronebotworkshop.com/technology/widget-weight-counter-using-hx711-and-led-display-feasibility-study/#post-46481

I hope it is self-explanatory, but obviously welcome questions, querying any 'deliberate' errors and so on.

Best wishes and good luck, Dave