QuickStart module
HShanko
Posts: 402
I have a question on schematic page 3. What is the function of Q1, D12 ahead of the 3.3v regulator? Seems the '5v' point would be closer to 4 volts.
Wish list: Wishing there were space for a RCA jack and resistors for TV output. But realize that would require more board space. I suppose one can use the headers to access required Prop pins and mount parts externally.
Wish list: Wishing there were space for a RCA jack and resistors for TV output. But realize that would require more board space. I suppose one can use the headers to access required Prop pins and mount parts externally.
Comments
I was looking for the information on QuickStart since its announcement, which was apparently before 2 April. Frustrating when this happens. Thanks for any assistance on this.
Do I recall correctly that there was some 'demo' code to be used with this board? Or was that just a nice dream?
QuickStart Examples:
http://www.parallaxsemiconductor.com/products/quickstart
Maybe I need to carefully read those 'examples'. Maybe there are demo source code there. I looked at one or two and they appeared to bring beginners up to speed.
Maybe I just hoped an demo to 'show off' the QuickStart module.
At first I tried to Brad's BST but couldn't find the Prop. Then went to Windows on the Mac and still wouldn't work. Shut down Parallels virtual engine and started over then things were OK. So went back to BST and 'woke up' to realize I'd downloaded the FTDI driver but hadn't installed it. Works now.
One question. When the Prop isn't running a program, all the LEDs light up if I touch the pcb opposite the Prop chip. Might this be due to I/Os being inputs when Prop not running? I noticed when I programmed the EEPROM with Lesson 6, it counted up and when done, if I held the pcb with fingers on both sides of the board at the Prop chip location all LEDs would be lit. And before FTDI was installed, even its LEDs would light up. Sure sounds like floating I/Os, to me.
Thank you Parallax for this cute Prop board design.
Anyone else get their QuickStart boards yet?
I'm the most biggest contributor for non-answers, but I can confirm that handling the QuickStart PCB on the back side could trigger the LEDs on the front because I noticed this myself. I'm pretty certain that you're touching the two traces that comprise the touch buttons. I'll ask David Carrier to jump in and explain what we're observing.
We're happy that you like the design!
Ken Gracey
The LEDs are driven by a buffer that connects to P16 through P23. The buffer is in place so the LEDs do not load the I/O pins. This also you to use the I/O pins for whatever you want, but still drive LEDs if you'd like. Since we didn't want to load the I/O pins, there aren't any pull-down resistors, so if you leave the I/O pins floating the input to the buffers will float. The 74HC541 tends to float low, so the LEDs are usually off, but you may see them all blink at once if you have noise on the power rails, or light randomly if you touch the I/O pins that connect to the buffer.
David Carrier
Parallax Inc.
-Phil
@ Phil, thanks for your view point too. I've always enjoyed your comments on any thread.
Now to get my fingertips on a diet to fit better and not hit two at once.
The LED driver chip inputs are floating, Prop I/O is in Input state, therefore nothing is driving the LED chip high or low, so one's body probably injects power line frequency 'noise' easily.
Apparently once a program runs and ends, the Prop returns to I/O input state. This was a new bit of info for me. Maybe I'm wrong; somebody have a better explanation?
repeat waitcnt(0)Thank you for that info and the 'hold pin state' suggestion. There is so much of a learning curve on the Prop, and so many features that Chip included in its design.
Regarding the '5v' power, for my setup I measured 5.13v input from the USB connector, with 0.03v, 5.13v and 5.13v on the three legs of D2 and 4.85v for that '5v' power with no additional loading on the board. That leaves 0.28v drop across D12; must be a Schottky device, not silicon or germanium. Answers my initial question.
I note at times the touchpad program, your 'jm_quickstart_demo.spin' in EEPROM doesn't seem to run. Yet later, without any prodding, it seems to be working again. Just by pressing the Reset switch can I invoke this effect. Is as if a counter has to 'wrap around' and then things are operating OK. Is this a missing initialization?
@ Jon, maybe it is just something weird on my board. I can touch one or more pads, do a Reset, and it might take many many seconds before the LEDs light up again. Maybe my fingers are too dry. I note this doesn't seem to happen if I wet my fingers. Guess I'm too high R.
I just noticed something else, good news. I left the board powered but slipped the bag it came in while out of the room for a couple of hours. Due to our three cats. I touched the outside of the bag just over the pads and the LEDs still worked OK. But not later on, like just after writing this! Yet now works OK again. At times. Capacitive effects?
Make sure you have the schematic from the bottom of the page at http://www.parallaxsemiconductor.com/products/quickstart; it should be titled "Rev A". You may be looking at a "Rev A2" schematic that I had posted earlier on the forums. The pinout of J1 has changed since the last prototype.
David Carrier
Parallax Inc.
I had A3 revision. I forgot I'd printed all I could find early on after the QuickStart was announced. Thanks. Time to print another set. And to make up an adapter for TV output.
One small detail missing is the page numbers, such as 1/3..3/3. Just a FYI. No biggie.
By the way, it is a bit confusing that this board is for sale on the old Parallax web site, but much more information exists on the ParallaxSemiconductor site. Seems there should be an obvious link between the two, NO?
Maybe it could be a bit more obvious, but the link is in the normal place on a product page where you look to get documents, schematics, etc.
My thoughts were the white strip was insulation for the backside of the touch buttons - to prevent inappropriate touching.
Rick
HShanko,
D12 is there to allow you to power the board from the VIN pin on the header without damaging the USB power circuit... If a USB cable is in place, power will come from the USB. If you want to "cut the cord", you can power the board from the VIN connection. D12 prevents current from passing from your VIN power connection into the USB circuit.
That's how I understand it anyway...
I've also had problems with Jon's Spin only version.
I modified the version with the PASM driver to eliminate the flicker.
I then tried out Jon's Spin version. It didn't seem to work as well. I also had to have slightly damp fingers in order for the LEDs to light up.
I finally found if I launched a new cog to monitor the touch pads I had much better results.
I'm attaching my version of Jon's Spin only code.
I've included notes on how to switch the driver to the PASM version. Either way uses a second cog.
@Jon, Let me know if there is a different way I should indicate this is a modified version of your code.
Duane
Since I asked I was told there was a later revision of the schematic. What was termed '5v' is now 'Vin'. Now it is clear; a diode to isolate the USB 5v from an externally applied voltage at 5v or greater. Wish there were a bit better explanation of what everything on the board is for. (From the writer's view, I realize it is difficult to anticipate what all user's will need/want to know about a circuit.)