Prop Plug and LQFP (Prop 1)
Greg LaPolla
Posts: 320
I have designed a PCB using the LQFP chip. In the past I have used the dip without any issues. Using the prop plug I get a timeout on the upload.
I have attached the schematic. I am converting an older controller from a 4 line lcd to a 2x3 touchscreen lcd. Also converted it from through hole to surface mount components. Do I need to put an actual usb port on the board with the lqfp chip or should this work ?
Thanks in advance!
I have attached the schematic. I am converting an older controller from a 4 line lcd to a 2x3 touchscreen lcd. Also converted it from through hole to surface mount components. Do I need to put an actual usb port on the board with the lqfp chip or should this work ?
Thanks in advance!
Comments
I'm probably a bit pull-up happy, but I'd be inclined to add a pull-up to the SCL line of the EE (mine and other libraries require it), and also on the SD pins so they're not floating when no card is inserted.
It looks like the you the emitters and collectors on your NPNs swapped. Am I wrong?
Can you share details on the touch-screen that you're going to use?
It appears the only thing using that 24-volt output are the relays. If so, what would you think about dropping the input voltage down, maybe to 12 volts, and using 12 volt relays?
Looks like a solid design otherwise!
Its just a simple ILI9341 based tft display off Ebay for around 12 bucks. Also you are correct on the transistors. I was just trying to figure out why the relays click on when power is applied. Looks like 20 bucks for the PCB's are down the drain.
I doubt you need pull-ups on your SD since these combo lcd modules normally put them on, even if you don't want them and I never use any, especially on the CS line since this the card's internal pull-up doubles as card detect. If you use EEPROM don't even bother with the original 32kB, just go to 64kB as that is standard these days and the extra 32kB can be handy for logging.
I'm sure you are aware of all the EMI and ground precautions when handling inductive loads such as relays and what they switch.
How'd ya get the transistors back-to-front?
BTW - if you show us your pcb artwork before you order, we might have a tip or two.
Look here for how it should be:
I now name the Prop-Plug nets USB_RX and USB_TX to keep things clear.
The problems I experienced were after moving to Diptrace and not paying attention.
It seems funny that 5 PCB's are $2 bucks and then $17 to ship!
I have moved away from Diptrace because it is to much of a hassle on a Mac. I now use KiCAD and I had to re-do the board and did not consult the propeller doc and just connected tx to tx and rx to rx.
I did make a few changes:
added pull-ups on miso and mosi on sd card and changed 5 volt regulator to one that has a max input of 30 volts just to be safe.
Thanks for the input!
Also new schematic is attached
If you are interested in the TFT display
here is where you can find it: 3.2 inch 240*320 TFT LCD Module Display with Touch Screen Panel SD Card Cage
I have used some objects from OBEX to get it all working: ILI9341 SPI driver and the touch object from: ILI9325 320x240 TFT driver
Yes, I don't trust internl pullups on reset and always put 10k there. I also learned from bad experience with one of my first boards with the P1 that the reset pin is very sensitive to glitches. So I always put a cap (10..100n) from /res to GND and as close to the chip as possible.
From 24vac you will see 34V peak! (24*sqrt(2)) From your voltage measurements, I would guess that your meter is reading average voltage. The diodes drop about 1v each, so the output of your rectifier would be 32v peak, 22v RMS, and 19.5v average. It would not be unusual to see 10% more voltage in some situations.
10uF is not really enough capacitance for the load of those relays. The datasheet says the coil is 576 ohms. Plugging that into the calculator here https://changpuak.ch/electronics/power_supply_design.php shows that with only 1 relay on, the capacitor voltage falls to 5v when the AC crosses zero.
Adding more capacitance would help somewhat. The problem will be that too much capacitance will result in the RMS voltage being more than 24v. A good solution might be to place a diode between the 24v net and C1. That would stop the relays from draining the capacitor during zero crossing. The relays should operate from the unfiltered bridge rectifier output just fine. It's unlikely they would release during zero crossing.
Another option would be to add a lot more capacitance on the rectifier output and use 5v relays. You'll definitely want a switching regulator for this setup, such as the R-78C5.0-1.0 Then your board could run off a wide range of input voltages.
Here is the the pcb and the schematic. Open to constructive criticisms and comments!
Thanks
Some pins appear to not connect to your not shown ground plane - this will most likely fry your props internal pll. You must fix this!
While certainly not mandatory, it is usual in I2C designs to have a pullup on both SDA and SCL pins. The props boot code always drives the SCL which is why some prop designs dont have an SCL pullup.
So unused pins should be grounded ?
All 4 ground pins are never "unused", they must all be connected to ground. It's not like all 4 pins are shorted together inside the package, they connect to various ground pads on the silicon and while you can get away with only connecting one during light testing, the chip will be compromised or damaged with these other grounds left floating. If it helps, think of the internal ground pins as being connected by very low but fusible resistance. You don't want parts of the chip to be damaged or misoperate when a bit more current is involved, so just ground them as they were designed to be.
As pointed out, that 10uF in the rectifier circuit is virtually useless. It is normal to have 1,000uF or so for the ripple filter but could be vary depending upon the peak current requirements.
P.S. Please use a 3-pin switching regulator to 5V or at least allow for it on the pcb. Using linears for such high voltages is just bad design unless you are still in the 80's in which case you just use great big regulators mounted on heat sinks.
BTW, I noticed that while your schematic shows all 4 pins grounded, your pcb does not conform. On the subject of schematics, try and orient the symbols in such a way that makes it easier to read the schematic. For instance, don't have the emitters of NPNs pointing up to a ground, point them instead, especially since it is a very easy thing to do.
All the gnd pins go to the gnd plane. I just turned pour off so you can see the traces. I was inquiring about unused prop pins should they go to gnd if not used ?
Edit: I see the VCC is not joined together if this other ones are the grounds. It's good to have a partial plane for the VCC too.
Got the boards yesterday. Everything working properly finally. Not bad for my first SMT board.
Made a few more design changes. As mentioned by several, I went with the recom 5v switcher and wow no heat! Also upped the caps on the power supply to 1000uf.
Using solder paste and a hot air rework station makes soldering a snap!
interesting display...
Enjoy,
Mike
This is a remake of a controller I made 10 years ago . that had a 4 line lcd. I just redesigned it to use smt instead of through hole components. I also removed the ADC because I changed temperature sensors and went from K type to a one wire based sensor, much easier to use and program for. I also dropped the PH sensor off as my ph sensor broke and it was very expensive to replace it. I see now looking on amazon that they are dirt cheap but I have to question the quality.
The only thing that I would like to do is rewrite the code in C, but I cant find a library to support the ili9341 chip that drives the tft screen and I really don't feel like writing one myself.
Enjoy!
Mike