Ray Leiter asked 3 years ago
On page 222 of the “LEARN ESP32 with Arduino IDE”, we find this statement:
“Since we’re using 12 LEDs, the maximum current is approximately 630 mA at full
brightness in white color”.
Nowhere am I able to find the basis for the 630 mA figure being chosen. If we compute 630/12, we get 52.5 mA!
Is it the case that each LED takes 52.5 mA? I can’t figure where that would come from.
Perhaps someone measured the current draw from the strip of 12 LEDs when they were set to the WHITE color?
Is that what happened? I have a 5 meter strip with 30 LEDs / meter which implies 150 LEDs. I did NOT count them!
I used my bench power supply to connect 5v DC to the strip connector BLACK wire and then I connected the other 3 pins (R,G,B) to ground and the entire strip lit up with what I’ll assume is WHITE!
I had a DMM inserted in series with the power supply and the max current I saw was approx. 300 mA!
Does that seem reasonable, given 30 LEDs per meter and a 5 meter strip?
I’m still struggling to find 3 of the same transistor (I have 1 of one kind and 2 of another and 3 of a kind that won’t support the current requirement.).
To solve that problem, I just ordered 6 N-channel power MOSFETs, 3 TIP120 Power Darlingtons and 10 2N2222s.
I wish I knew how to calculate the current draw for a strip of ‘n’ of my LEDs. Could it be as simple as N times I where N is the number of LEDs and I is the current draw for 1 LED?
An additional issue: It would be nice to have some instruction on how to go about the task of “converting” the recommended LED strip (5 meters worth of LEDs @ 30/meter) into a 12 LED strip as the author did. I’m guessing it’s considered to be rather obvious, but I’m always leery of the ‘obvious’. Anyway, here goes: I figure I’ll just cut the 12 off the end where the female connector is, rather than cutting at the ‘front’ where the controller plugs in.
That way, I’ll still have a ‘large’ strip I can use with the controller AND I’ll satisfy the need to have a 12 LED strip for the course. Note: the piece at the end where the female connector is will then be able to be connected either by soldering wires onto the copper pads OR using some kind of tiny wires that will fit the female connector.
If I screw it up, I’ll skip this unit of the course OR buy a smaller strip without a controller.
What are your thought on this matter?
Anyone?
Sara Santos Staff answered 3 years ago
Hi.
“Is it the case that each LED takes 52.5 mA? I can’t figure where that would come from.
Perhaps someone measured the current draw from the strip of 12 LEDs when they were set to the WHITE color?”
Yes, that was what happened.
The 300mA you got was for how many LEDs?
Here is a short explanation of maximum current draw (for a 12V led strip, it is similar for a 5V): https://learn.adafruit.com/rgb-led-strips/current-draw
The schematic diagram in this tutorial shows how to use a 12V LED strip: https://randomnerdtutorials.com/10-diy-wifi-rgb-led-mood-light-with-esp8266-step-by-step/
Regards,
Sara
Ray Leiter answered 3 years ago
Sara;
Thanks for the reply. I figured you guys got the current reading by inserting a meter in series with your supply of 12 LEDs — THAT is exactly what I did, only I used my ENTIRE strip (5 meters worth of LEDs @ 30 LEDSs/meter). That computes to 150 LEDs (As I mentioned, I did not count the LEDs on the entire strip, but I DID count how many LEDs were in 1 meter — and it was 30!).
My technique was to connect supply + to meter red lead, meter black lead to strip + (Black wire), then I connected supply ground to the other 3 strips leads (R, B, G). The entire strip lit up with what looked like WHITE and my meter showed approx. 300 mA. The only thing I can imagine was happening to give me that reading was I must have been using the current limiting function of the supply without realizing it?
I have read Adafruit’s article of computing current draw for the 12 v strips, many times — thanks for the reference.
The reference you give for the schematic diagram for the ESP8266 is pretty much the same as the schematic in Unit 10. I guess the problem I have is the omission of the designation of the transistor leads (EBC). I think it is probably assumed that when one looks at a TO92 transistor with the flat side facing the viewer, the lead arrangement is (left to right), EBC. However, that view does not always hold true — I have seen TO92’s where that arrangement was not the case!
AS FOR MY QUESTION regarding how/where to cut the strip, I decided to cut off the 12 LEDs I’m using for the course from the END of the strip. That way I can still use the larger part of the strip for something. I already made-up a special 4 pin connector so I could use the female connector that was factory installed and save myself having to cut off the connector and then solder wires to the copper pads. The 4-pin female connector requires 22 AWG wire (it’s close enough).
I am going to REPEAT my attempt to measure the current draw of the entire strip — I’ll let you know how I make out. Thanks again.
Steve Mercer answered 3 years ago
At 300mA for 150 LED’s that would be 2mA per LED. The whole strip would light up but would be very dim. Perhaps you misread the scale? It would make more sense that each LED would be drawing 20mA so the reading was 3A?
As for transistors, TO92 is just a package type. It’s not going to tell you the lead arrangement. You would use the data sheet of the device in question to find out its specific pin out.
Ray Leiter answered 3 years ago
Steve;
About the current draw on the LED strip;
I re-did the current measurement just this morning. Here is my result:
I used an adjustable power supply I got from Adafruit (Prod. # 4880) 3-12v DC out at 5A.
I used a Fluke 87-V DMM to measure the current drawn when I pressed the “White” button on the remote control unit.
The DMM showed 542 mA DC. Does that sound reasonable to you?
You’ll remember that Rui said he got approx. 600 mA for 12 LEDs! Given that — I wonder?
Could it be that the LEDs on my strip are some kind of ultra low power LEDs?
I bought them on Amazon at:
(https://www.amazon.com/dp/B091B61NL1?psc=1&ref=ppx_yo2_dt_b_product_details)
As for the transistors, I misspoke when I made it sound as though the TO designation had something to do with lead arrangement — I realize it doesn’t and is only referencing the physical packaging of the part. It is actually the manufacturer who determines lead arrangement. I was simply suggesting that the lead designations of ‘E’, ‘B’ and ‘C’ should somehow be shown on the pictorial schematic so its clear to beginners that the GPIO pins are driving the Base and the LED load is on the Collector. Perhaps I’m being too nitpicky — its just that such elementary details are often shown in other pictorial schematics.
At this point, I’m going to go ahead with this Unit of the course (Unit 10). (I’m using 2N2222’s).
Thanks for your help.
Sara Santos Staff answered 3 years ago
Hi Ray.
You are right, there are many details that we didn’t take into consideration.
We should revise that unit later, so it is not so confusing.
542 mA seems too low for such an amount of LEDs, but it can be a strip with different features, I’m not sure…
Regards,
Sara
Ray Leiter answered 3 years ago
Sara;
Thanks for your reply. I agree with you that a few details were omitted. It’s good to hear there will be a revision.
On this matter of the current draw:
I was having some trouble with 2 things: 1. my meters, 2. my brain.
The meters are OK if my brain would just let me remember how to use them correctly.
I was doing some dumb stuff when I was measuring the full strip current.
I think I’ve solved the problem: I was using the mA range on the meter an should have used the A range. When I did, this was my result: the full strip set to white showed 1180 mA, which would suggest each of the 150 LEDs takes approx. 8 mA. (still seems to be too low). However, when I cut off 12 LEDs from the end of the strip and set them to white, I got 230 mA, which suggests each LED took approx. 20 mA. I pretty much gave up on the measurements and then I hooked up the 12 LEDs to the ESP32 and ran the code you provided. It worked well. At this point, I’m studying the code for Units 10 & 11. I’m particularly interested in making sure I understand the Async Web Server. Thanks for all your help. I’ll have to look and see if RNTlabs has a course on Async web servers? Thanks, Ray
Sara Santos Staff answered 3 years ago
Hi Ray.
With the 12LEDs, you’re getting a reasonable value.
With the whole strip, it seems too low, but I’m not sure if that’s a “normal” behavior???
As for AsyncWeb Servers, our “Build Web Servers with the ESP32/ESP8266” eBook covers is exclusively dedicated to building web servers with the AsyncWebServer library.
We explain how to program the ESP boards, and how to build web pages to display readings and control outputs using HTML, CSS, and JavaScript. For a complete description of the ebook, you can check the following link:
Regards,
Sara