jeinzi
@jeinzi@discuss.tchncs.de
- Comment on SMD Component Identification 2 weeks ago:
I duckduckgoed “SOT23-6 boost converter” and found a picture of an IC with similar markings - I’m now pretty sure the component is an FP6291 switching regulator by Advanced Analog Electronics.
If you look at the datasheet, the “AL” identifies the part, and the following numbers are the year of production and the wafer lot number, so they could really be anything. The pinout matches as well, given a few inaccuracies in your schematic, which I think I can confirm on the images. Thanks for the image of the PCB against the light, that was very helpful. Pin 1 would be on the bottom right, connected to the inductor L1 to boost the voltage, with the other pins arranged counter-clockwise. Pin 2 should then be connected to your PCB ground; to confirm, you could use a multimeter in continuity mode to measure to the BAT- and 5- connections. The right side of R4 should also be connected to ground, and 24 kΩ would set the current limit of the IC to 2A (page 7). On pin three is one of the mistakes in your schematic as far as I can tell, I think that pin is really connected to the point between R6 and R5, for output voltage feedback. I also think R6 is meant to read “84D”, which would be the resistor code for 732 kΩ with 1% tolerance. If you calculate the output voltage of the regulator with the 0.6V feedback voltage from the datasheet and 732k/100k resistors, it comes out to 4.99V, which would be compatible with the USB 5+/5- stuff. Connecting EN to VCC (pin 4 to 5) is also common to permanently enable an IC, but I think there’s another error in your schematic: I’m pretty sure those two pins are directly connected to BAT+ instead of through C4, and that C4 instead connects from those two pins to ground to stabilize the input voltage.
- Comment on SMD Component Identification 2 weeks ago:
There’s no way U1 is charging the battery. How would it? If the connection labeled USB is the power source, it’s only connection to U1 is through a 100k resistor and a reverse biased diode. Also, charging AA batteries? Sure, you could plug in some NiMH cells, but then the device would need to have explicit instructions telling you that this is indeed a charger and to only ever insert rechargable AA battery cells.
- Comment on SMD Component Identification 2 weeks ago:
Feels an awful lot like a step-up converter. I’m missing the ground connection though and potentially a connection to a voltage divider for feedback. Where does R4 lead to? Are you sure there is no connection from the middle right pin except to C3? Is pin 1 of U1 marked? Can you make a detailled photo of the IC to better identify the text on it?
- Comment on Request for comments: USB C "trigger board" 4 weeks ago:
tl;dr: I’m reasonably sure this will work as is.
The following comments involving my personal opinions might be most useful for more complex projects:
While I also try to isolate building blocks in my schematics, I think it’s sometimes beneficial to have some visible connections using wires. Your schematic isn’t very complex, but I still needed to jump around a bit to understand how current flows from the USB connection to the output. I would arrange the building blocks so that current flows from left to right and include one wire that starts at the USB jack, passes by the CH224K and its bypass cap, through the FET to the terminal block, so you can read the current flow like you would a line of text.
Layout:
- Before manufacturing, better before starting the layout, I would include the design rules of your manufacturer under File > Board Setup > Design Rules > Constraints. Currently you haven’t defined minimal clearances, widths etc. Google “[your preferred manufacturer] capabilities”. You might also find existing KiCad templates that you can import.
- I would place the reference designators on the silkscreen so they are visible after assembly, to help with debugging and repairability.
- I would also take care that everything you want to show is legible; currently, your JP-labels overlap U1
- To find enough room on the silkscreen, you could probably reduce your text size. Look up the minimum in your manufacturer capabilities; in addition to putting those values into your design rules, you can also add them in File > Board Setup > Text & Graphics > Defaults > Silk Layers. Apart from that being the new standard, you can then also easily go to Edit > Edit Text & Graphics Properties to set all existing reference designators to those new default values. In my personal experience (with JLCPCB at least), the text also stays legible waayyy below the quoted minimum size.
- I make it a point to include some metadata on all my PCBs; a version number, date, a project title and the name of the designer, so I don’t confuse myself or others when the PCB is found some years later in a random box.
- I like your package size for the passive resistors and caps, but if you have space issues, you will probably have no issue soldering the smaller 0805 packages by hand either. We regularly have discussions what size can comfortably soldered without magnification; one of my colleagues insists that even 0603 is comfortable.
Regarding both the schematic and layout: run the ERC/DRC and fix all errors and warnings. Most of it is noise, but hidden beneath that, serious issues can hide.
Another idea that might be out of scope for your project: You could add optional 5.1k pull-down resistors on the CC lines and a solder jumper from VBUS to VOUT. Then you could use the board even without the CH244K and the FET if you only need 5V.
- Comment on Disconnect wire to close a switch with a simple circuit 2 months ago:
With a PMOS device used for simple on/off switching, placing the load between drain and ground would be correct. With an NMOS FET, the load should be between drain and VCC.
In general: NMOS source to GND, PMOS source to VCC.
- Comment on Disconnect wire to close a switch with a simple circuit 2 months ago:
Props for the detailled answer, but this all sounds completely backwards.
Low-side switching should in general use an N-Channel FET. And with your voltage divider, the gate will be at 6% auf the supply voltage, not 94%, which means the FET will always be conducting. It will also never fully turn on, because that would mean the Gate-Source voltage would drop to near 0, which would turn it off again.
My counter proposal:
- Comment on Microcontroller recommendations for a weather station 2 months ago:
I noticed that I glossed over your breadboard requirement. If you want to use something like an ATtiny or CH32, you could always buy some generic SMD breakouts like this. Both of these microcontroller series have internal oscillators and flash memories, so you really don’t need any external components. Maybe a bypass capacitor for good measure.
- Comment on Microcontroller recommendations for a weather station 2 months ago:
If networking is the goal, choose any ESP32 module. If you want something simple akin to an ATtiny, ich can recommend the CH32V003. Is has plenty pins and an I²C peripheral, costs around 15 ct. For accurate timing, add an external oscillator instead of using the internal one.
- Comment on USB PD for older device 6 months ago:
I’m not sure about the standard - but in my experience, if a PD trigger IC requests 12V, that will be supplied, no matter the current draw. I have used this to power several low power devices, for example a 12V computer fan, and I have also verified this with no load at all. There is also PD PPS, which could be used to deliver 14V or any other voltage.
- Comment on Is SPI just "slow"? 8 months ago:
I noticed that you use digitalWrite multiple times for each transmitted pixel. That function is pretty slow - you should instead manipulate the microcontrollers registers directly for maximum performance. If you are using an Arduino, this article will help: roboticsbackend.com/arduino-fast-digitalwrite/
