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Messages - dps

16
Project logs / Re: A/C Energy Saver
YES! Such a project has been on my "maybe to-do" list for quite some time. Mine would support precise on and off times (multiple) and an onboard thermometer for better thermostat-ing.

Maybe some day... which probably will end up being after I no longer have a window A/C that needs the remote! :p
17
General discussion / Re: Cheap PCB manufacturing timelines
Seeed Studio, 100mm by 100mm, March 2011:

On the front, many vias are drilled too far "south" relative to the copper.  Actually, that's true for most of the drilled holes.  The back looks decent.

Edit: There also are vias featuring a drill size much smaller than the copper.  This was a design problem, not a manufacturing problem.  :-)

Edit2: Grammar and numeric errors fixed.  I can't believe I typed "to" instead of "too"!

Image license: CC BY-SA
18
Open Bench Logic Sniffer / Re: Why should I buy?
I use a Logic16, and it's a very nice tool!  The hardware is of excellent quality and works very well.  The software is well-polished as well and has met my needs so far.  Their customer support is excellent, too.

<aside>
They very recently added DMX512 decoding to the software, which made me happy.  I don't do any DMX512 work any more, but years ago I built a DMX512 console for a friend who used it to control a set of moving lights in his DJ (?) work.  Good times!  :-)
</aside>
19
Web platform / Re: Suitable relays
Don't forget the flyback diode so you don't fry your transistor (BJT or MOSFET) when it turns off the relay!
20
Project logs / Re: Door lock reminder
[quote author="pppd"]I don't know about you guys but I constantly catch myself wondering whether I have locked my apartment door or not.[/quote]
I totally can relate.  Every time I go back to check, of course my door is locked.  :-)

Although, it has been a while since I've done this.
22
Bus Blaster JTAG debugger / Fried, then fixed
The other day, I fried my Bus Blaster.  The 20-pin cable I bought did not have polarizing keys.  I noticed this before I started using the device and figured I'd always be careful about which direction I plugged in the cable.  Bad assumption!

That fateful day I plugged the cable in backwards.  I noticed that the CPLD was getting hot (and perhaps the FTDI chip too).  I quickly unplugged the cable, but unfortunately the Bus Blaster was toast!  I quickly ordered another JTAG pod to keep my work going until I could fix the BB.

I desoldered the CPLD from the BB using my trusty SparkFun Heaterizer XL-3000.  When I plugged the BB into my computer, I was able to connect to the FT2232!  So the FTDI chip seems fine.

Today I received a replacement CPLD (and a new 20-pin cable WITH a polarizing key) from Digi-Key.  I soldered the new CPLD on my BB, compiled urJTAG from source, and loaded the JTAGKey buffer configuration into the CPLD.  I tested my new (if slightly toasted) Bus Blaster on an ARM development board, and I was able to halt and reset the processor!  Success!

Moral of the story: ALWAYS use cables with polarizing keys.  I bought the H3DDH-2006G-ND, which includes both a polarizing key and strain relief.  (Digi-Key shows this and similar cables as "Value Added Items," which means that they prepare these cables on-demand when ordered.  Mine shipped the same day with the rest of my order.)


tl;dr
Use cables with polarizing keys.  Cables without polarizing keys destroy your devices, time, and satisfaction.
23
Open 7400 Competition / Re: [Entry] full-featured SNES controller
[quote author="Lint"]In fact, if anyone ever reproduce my controller and is within 150ms from me, please contact me for a Rock n' Roll Racing extravaganza.[/quote]

150ms?  I.e. 150 millisecond ping time?  150 meters?  :-)
26
General discussion / Re: selecting a microcontroller
Check out the ADuC702x [1] series from Analog Devices.  I've used them before, and they work well (but note the errata when you start using the A/D, as there is a "gotcha" in starting the conversion).  They're based on the ARM7TDMI processor and have several sleep modes for decreased power consumption.

Not sure about low power or open-source toolchains, though.  Keil has a free version of their IDE [2] that supports up to 32KB of Flash.  Hmm.  Perhaps downloading uVision isn't as easy as it used to be (or perhaps my memory is faulty).  I guess their new IDE is MDK-ARM [3].

[1] http://www.analog.com/en/processors-dsp ... oduct.html
[2] http://www.keil.com/uvision/
[3] http://www.keil.com/arm/mdk.asp
27
Project development, ideas, and suggestions / Re: PCF8593 RTC board
@chortik, yep, that's exactly what I had in mind!

[quote author="chortik"]BTW, what about only using a diode with forward voltage of .6V to feed the supercap?[/quote]
That possibly would work, but you would have no wiggle room for either VCC > 3.3V or Vf < 0.6V.  You'd have to take a look at the datasheet for the diode to see the possible range on forward voltage (as it varies by current through the device).

Another option would be to use two supercaps in series and a rail-to-rail op amp to balance the charge on the two caps.  The key is finding the appropriate op amp that works down to such low voltages while still keeping the rail-to-rail-ness.
I built such a circuit as part of a Christmas present to my wife: an automatic trunk light for our car.  I don't remember what particular op amp I used, though.
28
Project development, ideas, and suggestions / Re: PCF8593 RTC board
[quote author="chortik"]@dps, how would I connect the cap back to the IC?[/quote]
Ah, connect "SuperCap" directly to the IC's VDD.

VCC ---///--- V1 ---///--- GND,
V1 ---|>|--- SuperCap --- GND
SuperCap --- IC pin 8

When VCC is connected, it will directly charge the supercap, and the supercap will power the IC.  Kind of like a proper UPS.

However, watch out for the voltage drop over the diode.  You can tweak the values of the resistors to get the proper maximum voltage.

Hmm.  I wonder if this will work...  How much current does the IC pull while it is being accessed?  You might need to keep your dual-diode:  SuperCap ---|>|--- Pin8 ---|<|--- VCC

I worry about the sudden change in voltage on Pin8, though.  You do have a bypass cap, which should help a bit.

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