Schematic review / suggestions (Space Blaster) - Page 1
Forum section: electronics / projects

author: Youkai
author_rank: Regular Contributor
timestamp: March 20, 2023, 03:52:53 am
content: I'm working on the electronics for my project now and I've put together this preliminary schematic. Please review and provide comments/suggestions. Any errors/problems you see with the provided schematic obviously; but I'm also interested in any suggestions you might have for substitutions or better ways to accomplish the same results.The servo's will be (5) HS-55 and (1) HS-311. There will be about a meter of DotStar; i.e. 60 RGB LED's.I'm not sure what the battery pack is yet. I haven't even tried to calculate power needs (not that I know how) since I'm still not sure if the components in the diagram are final.

author: Buriedcode
author_rank: Super Contributor
timestamp: March 20, 2023, 08:04:06 pm
content: Not a full critique of the schematic but a couple of observations at a glance:1) The diode after the buck converter will drop some voltage depending on current. Whilst the PWM board probably won't take much current, the DFplayer might take a bit more, and the "dotstar" LEDs will certainly take a lot of current. for 60 LED's assuming they're all white, maxed out, thats 60 * 60mA = 3.6A. Even if that schottky diode could cope with that current it will no doubt drop significant voltage, so the it will be much less than 5V. If we assume you don't put all the LEDs on at the same time, or they're all white it will of course be much lower, but even at ~1.5A it'll drop probably >0.5V so if the buck outputs 5V, it'll only be 4.5V after the diode - can the PWM board cope with that?Also, if you raise the bucks output voltage to say 5.5V to couter-act that drop, the diodes drop depends on current - which depends on what the LEDs are doing, so its dynamic, and could mean, with all LED's off the diode only drops ~0.2V. So it outputs 5.3V.Ultimately I would power the LED's off the buck, and the lower-part parts off either a lienar regulator, or a second buck.And the servos? They'll obviously take some current when they're operating too. I say - power the "big stuff" (servos/LEDs) with their own setup, and the "brains" (low power boards) from another.2) The pro micro (sparkfun, or official Arduino) have on board regulators that have a maximum input voltage of 16V. I'm assuming you don't intend to use a battery pack with a higher voltage, but beware, some pro micro clones use sot23 regulators that only cope with a maximum of 9V in.Secondary stuff:1) For prototyping, I would add some small value series resistors to the buttons (100 - 330R?). These make no difference to the operation, but they mean that, if you make an error with the firmware and accidently make these GPIO's outputs, and high, pressing the buttons won't short these IO to ground possibly destroying the IO pins driver. I don't think I've managed to actually do that with a pro micro, but its purely a precautionary measure - the resistors can be shorted or removed afterwards even though they don't actually do any harm.2) I'm sure that the pro micro, the PWM board and DFplayer have their own decoupling caps on board, but adding one per board wont' hurt providing they're not stupidly high value (even 10-47uF is fine, unless they are powered by a very noisy buck that needs 470uF).3) It looks like you've got quite a lot of stuff to power, so the battery will likely be large - soquiescent(standby current) probably isn't a concern. But if you plan on leaving this powered up but not actually "doing anything" then all those modules could add up to drawing enough power to drain the battery quicker. Again, we're probabyl talking a max of what, 20-50mA? But for a small battery that can mean only a few hours of standby. If the whole thing has a main on/off switch on the battery then this doesn't matter!Edit: so many typos...

author: Youkai
author_rank: Regular Contributor
timestamp: March 20, 2023, 08:12:19 pm
content: Thanks for the reply Buriedcode. I'll try to digest it more later. The plan for this is for it to be a cosplay prop. Once I nail down the power requirements I'm hoping I can find a battery that will allow it to run for 1-2 hours. There is no need for it to be in stand-by when the person isn't actually wearing it and they could turn it off any time they aren't in a place where it's functions are useful/interesting.

author: Youkai
author_rank: Regular Contributor
timestamp: April 01, 2023, 07:13:35 pm
content: Ok back at it again finally. Some notes on the changes:Split the Servo/LED and other stuff per recommendation. They are on separate bucks now so high drain won't affect the pro micro.I read that the internal pull-ups can be janky so I'm putting an external one in. Is it ok to run all the buttons off the one resistor like I did?There will be 60-ish LED total but most of the time only 5-10 of them will be on and the will not be white. There will be at time when they are all on using a bright purple/blue color. At that time the color will be pulsing in intensity. I can set it up so that the pulse travels in waves to reduce current need (rather than having them all pulse brighter at the same time.The servos will be mostly stationary. If it's possible there are times I'd like to make the 5 smaller ones all move at the same time but I could easily write the code such that only two move at a time in sequence.Any thoughts or comments on the current schematic before I try and calculate power consumption?

author: Buriedcode
author_rank: Super Contributor
timestamp: April 02, 2023, 01:06:26 am
content: Quote from: Youkai on April 01, 2023, 07:13:35 pmQuote from: Youkai on April 01, 2023, 07:13:35 pmNo. Look at the connections, and ask yourself what happens when one pressing a button - what happens to the other GPIO when a button pulls that to GND?I haven't heard anything about internal pullups being janky, but it certainly doesn't hurt to use external ones. Value is pretty unimportant, it's jsut there to stop the IO floating and hold the pin in a known state (in this case, high/1/VCC). As inputs have such a massive input impedance, noise can trigger floating inputs, it really doesn't take much current to hold it high, 10k-60k is common, and won't waste much pwer when pulled to ground.Quote from: Youkai on April 01, 2023, 07:13:35 pmIt looks like thoser DOTstar LEDs are different from the usual adressable ones, in that they require a clock and data line. This generally makes no difference except that, I can see a small possibility that it makes it slightly easier to "accidently" turn on all the LEDs in software - but you'd probably have to screw something up a fair bit to do that. Initialising them on start up as all OFF is good practice, even if they are designed to be OFF on power up.As long as you're aware of this, and have a rough idea of how many LEDs will be on at any given time and what brightness/colour, you can get an easy rough idea of the current draw. Having "waves" is a good call, plus it looks niceQuote from: Youkai on April 01, 2023, 07:13:35 pmI guess you could measure this, but it would be difficult to measure current accurately with a multimeter for things that occur briefly, like moving a servo (multimeteres have quite a long settling time). I'd say just do what you need it to do, and keep an eye on the supply to the servos whilst its running your program (or the rest of the "high current" stuff) and if it starts to sag when everything is busy, you know you're drawing too much. A quick test before putting it all together doesn't hurt.Quote from: Youkai on April 01, 2023, 07:13:35 pmYes.1. The 3A diodes, will just waste power and drop the bucks output voltage - your buck converters should regulate voltage pretty well on their own, and diodes shouldn't be necessary - unless you're powering the same stuff fom multiple sources, in which case diodes are required to stop one power supply interfering with the other.The diode on the right, powering the pro micro and DF player is probably ok, since neither of those will draw significant current - and so its voltage drop will be quite small for a schottky, but sitll unecessary.2. I assume the left buck converter is also powering the servos? Don't see any connections on the schem.3. You're using I2C (SDA/SCL) to control the PWM board (PCA9685) - does that board have pullups on the I2C lines? (I just quickly googled for similar boards, seems they include the pullups on board!).4. As current draw can change very rapidly on dot-star/addressable LEDs - for example going from all OFF(0mA) to say, 20 purple (2x20mA * 20 = 800mA!) Some find a largish capacitor across the LED strips power rails close to the connector/strip prevents glitches/dips in power when this happens. 1000uF seems overkill to me, but its recommended on the Adafruit website.5. Not on the schematic, but there are many buck converter modules about. Many have overblown claims over current capacity, and pretty poor decoupling capacitors on the input and output. This means that their output can sag under loads that *should* be OK. A quick test before you put all the system together - but say running some of those LED's, and moving servos whilst monitoring the bucks output voltage with a meter would be prudent. This is less critical for the right buck converter which has to provide much less current.thats all I can see, but another pair of eyes will be handy - we all miss obvious things sometimes.

author: Youkai
author_rank: Regular Contributor
timestamp: April 02, 2023, 05:27:59 pm
content: Quote from: Buriedcode on April 02, 2023, 01:06:26 amThose are an artifact of a previous project I worked on. I forget why it was recommended that I put them in. If the aren't necessary I'll remove them.Quote from: Buriedcode on April 02, 2023, 01:06:26 amAll three wires of the servos are going to the PWM board. They are getting power from "V+" of the board.Quote from: Buriedcode on April 02, 2023, 01:06:26 amThere is the 1000uf capacitor near the buck and the second one on the PWM board. I guess you could kind of think of the one near the buck as the "LED capacitor". Though the way I have it, it's in series with the servos so it's doing double duty. Questions for you 1) Do I need both? (if not I'll remove PWM one) 2) If so should I move the one near the buck so it's parallel to the PWM board (i.e. serving the LED only)?Here's the updated schematic. Thanks for your help!

author: abeyer
author_rank: Frequent Contributor
timestamp: April 02, 2023, 07:01:51 pm
content: Quote from: Youkai on April 02, 2023, 05:27:59 pmBut the V+ supply doesn't appear to be connected to anything?Nevermind, I missed the supply on the side and just saw the NC'd V+ at the ends...so yes, the left buck is the servo supply through the V+ rail on the PWM board.