Odd display voltage problem. (and forum frustration!) - Page 1
Forum section: electronics / beginners

author: msknight
author_rank: Regular Contributor
timestamp: June 06, 2018, 05:36:45 pm
content: Been looking for a 5v 5"-ish display to hook up to the composite output from my GoPro and power from a USB line.I managed to find this, (picture hopefully attached) which looks like a converted 12v car display... which I believe someone has altered. Although how, I can't see. Anyway, it failed with an out of sync display. The seller sent me a replacement, but that doesn't work either.Back to this display... I used a Chinese DC transformer to up the line to about 7v... and then it worked. All fine and dandy... but the transformer screams like a mini-banshee.I've got no clue how to take this forward. Any advice would be gratefully appreciated.Incidentally, I attached my jpeg image, and then the system said I couldn't post. Only jpg allowed. So I returned to the post, renamed the image, and then did a post to be told that I had already posted less than 30 seconds ago. So they I waited the required 30 seconds and submitted again... and was then told that I'd already posted this topic... but I can't see it. Please... somebody save me!) - (I had to create a new post and cut-paste everything over. *sigh*)

author: Brumby
author_rank: Unknown
timestamp: June 07, 2018, 02:30:58 am
content: Quote from: msknight on June 06, 2018, 05:36:45 pmUnfortunately there is a distinction between jpeg and jpg, but you now know how to get around that - just rename. The 30 second wait is to make sure nobody can flood the site with posts in a short time.The "already posted" message comes from the fact that you clicked on "Post" on the same page that you had already clicked on "Post". You need to do a refresh or navigate away to clear that and you will be fine. Just make sure you copy your text if you don't want to re-type it.I know this is a bit of a false condition because the original attempt to post wasn't successful - but somewhere there is a flag set when you try and this is what causes the problem. Reloading the page clears it and you can go again. I think most of us have encountered this. We just cuss and do the refresh. If we forget to copy the text, we cuss some more - especially if it was a significant body of text.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: June 07, 2018, 02:57:03 am
content: Maybe your "DC transformer" (DC-DC boost converter?) can't deliver the required current?

author: amyk
author_rank: Super Contributor
timestamp: June 07, 2018, 03:44:19 am
content: 7V is right around the dropout voltage for a standard 5V linear (non-LDO) regulator... although I see 3 switching regulators on the board, those have a minimum input voltage too. The AMT630A uses 3.3V, but something else on the board might need 5V. First thing to do is determine what those regulators are and their output voltages.

author: msknight
author_rank: Regular Contributor
timestamp: June 07, 2018, 04:29:15 am
content: Thanks for the feedback folks.Looking at this, I think my best option at the moment, is to look at another way to get the input up to 7v and not to try and get too heavy. I'd be grateful for advice on approaches on this please, that will not be too "high". My USB current meters haven't arrived yet (nor my EEV multi, which is on the way) so I can't detail any power draw, but I don't think it's that much.

author: TonyCheungHKG
author_rank: Newbie
timestamp: April 09, 2020, 10:40:47 am
content: I found this topic during google search. It has been a long time but I wanted to share it. Maybe someone still needs it. The working voltage of the circuit is 3.3V and the Backlight is 5V. If you wish, you can directly drive by 5V bypassing the XL1509 (TD1509) circuit at the input.You may download AMT630A recommended application schematics from herehttps://tigermagnetics.com/zip/AMT630_demo_schematics.rar.

author: msknight
author_rank: Regular Contributor
timestamp: June 21, 2020, 03:40:25 pm
content: Quote from: TonyCheungHKG on April 09, 2020, 10:40:47 amThanks very much! That helps a lot.