While working on my Pico-based handheld (https://savagechats.com/index.php?topic=295.0 (https://savagechats.com/index.php?topic=295.0)) I was considering the CrowPanel 3.5"-480*320 HMI Pico RP2040 Touchscreen. One of the troubles that I had with that was that there is no actual power switch - it remains on all the time - not good for long-time usage on battery. It hit me that maybe I don't actually need to turn the thing off, but rather just put it into a low-power mode.
First thing to try was to dim the display. So, BACKLIGHT 0, and that darkened the display. But was that actually off? So, while it was in low-backlight mode, I pulled the plug (I don't have the battery connected at this time) bingo - I could not see any difference between LCD off, and entire thing off.
So, wanting to see how much current the thing drew while the LCD was on, and off, I started looking for a USB cable that had (or I could make) a cut in the +Vcc wire. With that I would be able to wire in banana plugs for my DMM, to read Amps (or more accurately, mA 8) ) While searching on my favorite cash drain, I found these little USB DMMs (well voltage and current.) The best part is that they were two for $10, delivered (with Prime): https://www.amazon.com/dp/B0CJTJXWG1?ref=ppx_yo2ov_dt_b_fed_asin_title .
Here you can see the current draw while the display is at full on (BACKLIGHT 100):
(https://files.granzeier.com/Downloads/SavageCircuits/Meter-Pico-On.jpg)
You can see that the "handheld" display is on, and the ammeter shows a draw of 0.13A - yeah, this thing goes up to 3 full amps!
Here you can see the current draw while the display is at off (BACKLIGHT 0):
(https://files.granzeier.com/Downloads/SavageCircuits/Meter-Pico-Off.jpg)
0.04A (or 40 mA) - not exactly low-power, but one-third the current of the display at full.
When I plugged the battery into the handheld, the current went up to 0.31 amps! Well, at least it is only while charging the battery, and not while in use.
Anyway - I wanted to let you guys know about these USB meters, at $5 each delivered (in twos,) they will come in handy for testing/playing with USB devices.
Very informative, granz. I have several different USB meters from Amazon.
20250331_224806.jpg
Here are three, the fourth is at work, so I can't take a photo of it at the moment. I sometimes use them for testing USB device current / voltage, especially for various phone chargers.
20250331_225555.jpg
This one looks like yours, granz. ;)
20250331_225433.jpg
This is the same brand, but only one port and LCD instead of LED display.
20250331_225401.jpg
This MakerHawk USB Multimeter (https://a.co/d/hVpYHie) has USB-C and some more advanced functions.
https://www.lowes.com/pd/Klein-Tools-Lcd-Specialty-Meter/5014634539 (https://www.lowes.com/pd/Klein-Tools-Lcd-Specialty-Meter/5014634539)
This is what I have, though mine, wherever it is at the moment, is the older just Reg USB ver, it don't uave USB-C at all. Works pretty well.
EDIT:https://www.kleintools.com/catalog/usb-digital-meters/usb-digital-meter-usb-type (https://www.kleintools.com/catalog/usb-digital-meters/usb-digital-meter-usb-type)
This is the one I have.
Quote from: JKnightandKARR on Apr 01, 2025, 12:14 PMThis is what I have, though mine, wherever it is at the moment, is the older just Reg USB ver, it don't uave USB-C at all. Works pretty well.
The first two I posted don't have USB-C, but there's been a surge of everything having USB-C. My last three phones had USB-C. My new car has USB-C chargers AND the media plug. I've been using a USB Thumb Drive for years with my whole music collection on it. I had to order a USB-C Thumb Drive (https://a.co/d/9zgrKbU) and then transfer the music to it, because my new car does NOT have a USB-A connector. :o
Quote from: Chris Savage on Apr 01, 2025, 01:23 PMQuote from: JKnightandKARR on Apr 01, 2025, 12:14 PMThis is what I have, though mine, wherever it is at the moment, is the older just Reg USB ver, it don't uave USB-C at all. Works pretty well.
The first two I posted don't have USB-C, but there's been a surge of everything having USB-C. My last three phones had USB-C. My new car has USB-C chargers AND the media plug. I've been using a USB Thumb Drive for years with my whole music collection on it. I had to order a USB-C Thumb Drive (https://a.co/d/9zgrKbU) and then transfer the music to it, because my new car does NOT have a USB-A connector. :o
Anymore alot does have USB-C, my Acer Nitro 5 and my ASUS motherboard in my desktop both have it, along with my Sony wireless headphones. Might not hurt to get a new one that does have USB-A/C ports.
Quote from: Chris Savage on Mar 31, 2025, 10:51 PM...20250331_225401.jpg
This MakerHawk USB Multimeter (https://a.co/d/hVpYHie) has USB-C and some more advanced functions.
That MakerHawk looks like a great meter. But, when I went to the URL that you provided, Amazon has another option - one that goes out to 4 places past the decimal point (tenths of a volt, and tenths of a volt - better for low-power wearable stuff.) It's $35, but much better specs. I sold the Epson notebook, so as soon as I get the money in my bank, I will be ordering that one.
While the FNB48 is much better specs, I am not disappointed in the Keweisi meters - they are incredibly low cost (one seventh the cost,) and do what they claim to do.
Quote from: granz on Apr 02, 2025, 11:48 AMWhile the FNB48 is much better specs, I am not disappointed in the Keweisi meters - they are incredibly low cost (one seventh the cost,) and do what they claim to do.
That's why I have a mix...sometimes you just need quick and easy. Sometimes you need more.