User jluciani - Chiphacker

Answer by jluciani for Connecting arduino and separate power supply grounds

2010-08-01T01:55:30Z

If the supplies are electrically isolated then the grounds can be connected. If you are not sure you have isolated supplies I would not connect them.

Another option is to use optical isolators and keep the grounds separate. This can be quite a few additional parts but is a very safe way to interface circuits.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Good high-lumen LED suppliers?

2010-08-01T01:50:32Z

The Cree XLamp datasheet looks fairly complete. I just finished a job that used 36 XLamp (3W) LEDs and the Cree devices seem to work quite well. IIRC there was a lumen/current curve in the datasheet.

Not sure about other manufacturers (or part numbers) but the thermal pad of the XLamp is electrically neutral making the thermal management a lot easier.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Best/Favorite/Unique dev kits

2010-07-31T23:18:54Z

I make a development kit called the NB2AS that has the following features --

ATmega644P + RTC + uSD + 2ch/12bit DAC
Altoids form factor
Single I/O connector that enables you to mount peripherals in the same plane, stacked vertically, using a backplane or with a ribbon cable.
Peripherals include a prototyping board, Li-ion charger, and screw terminal board.

See http://wiblocks.luciani.org/NB2/NB2AS-index.html

The board is compatible with the Arduino+Sanguino tools but you can use it as an Atmel development board with avr-gcc. I usually develop with avr-gcc + Make.

I have other boards on the site and in the works but since the first specification in your list was form-factor I mentioned the NB2AS.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Daytime viewable LCDs

2010-07-31T00:13:08Z

The only displays that I would consider daytime viewable are organic LEDs. Expensive but excellent contrast and saturated colors.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for How do I calculate the thermal resistance of aluminum flat stock

2010-07-30T14:50:04Z

You will probably need a very large plate or a fair amount of moving air.

What is the on-time of the TIP122? If the on-time is greater than 100mS then you are dissipating 72W not 36W. You need to look at the transient thermal response curves to determine the derating.

You need to allow some thermal resistance for the interface between the case of the transistor and the sink (or plate).

Assuming that your on-time is less than 1mS you are dissipating 36W. Looking at the On-Semi datasheet --

Rjc = 1.92 degC/W max. Absolute maximum junction temperature = 150degC (I would not exceed 125degC)

T = (Rjc + Rcs + Rsa) * Pd

125 = (1.92 + 0.5 + Rsa) * 36

Rsa = 1.05degC/W (which agrees with your calculation when you subtract Rcs)

If you take a look at the heatsink vendors datasheets you can get an idea of sizes. Checkout http://www.aavidthermalloy.com/

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for What is a differential ADC?

2010-07-27T00:14:32Z

A differential ADC will measure the voltage difference between two pins (the plus and minus input). A single-ended ("regular") ADC will measure the voltage difference between one pin and ground.

A lot of differential ADCs can be configured to give you twice the channels in single-ended mode.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Delayed power supply startup

2010-07-26T12:12:07Z

You may want to search for "power supply sequencers" and "powerpath controllers" at Linear Technology, Maxim and TI. Those devices integrate a variety of sequencing and control functions including on/off, delay start, sequencing of multiple supplies. Some have integrated FETs.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Is it safe to use a DC power adapter that isn't UL Listed or CSA certified?

2010-07-26T01:23:15Z

There are a variety of design, manufacturing and qualification requirements to meet UL, CSA and TUV. I would not use a line powered supply that does not meet these specifications.

I also tend to buy these supplies from name brand manufacturers and manufacturers that have ISO9000 approval even though it is difficult to know how/where a device was manufactured.

I would try to return the supply.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for What's the best way to store and categorise resistors/capacitors/ICs/etc?

2010-07-18T21:52:40Z

For TH and larger parts I use lots of small drawers. I also use the Akro-mils cabinets with dividers. http://www.amazon.com/gp/product/B00018AR5Y/192-5968131-0652527 These are nice because you can different draw sizes in a 17"x11"x11" cabinet. Very expensive unless you can find them surplus.

For SMD components I use a combination of stainless steel tins and watchmakers tins. I built some low-profile trays that hold the tins. See http://www.luciani.org/no-place-to-go/comp-storage/index.html

One very nice thing about the tins is they are small. For most designs you can kit up the different components on your bench.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Software to create timing diagrams

2010-07-17T16:54:59Z

The tool that I have bookmarked is -- http://www.timingtool.com/menu/tour/ttmain.php I have not tried it or taken a close look.

If you are using TeX and friends there is a timing package for the tikz picture environment (check CTAN). Sometimes with the TeX tools you can find wrapper scripts or GUIs that can create standalone images.

The documentation on the tikz-timing package is at http://www.tug.org/texmf-dist/doc/latex/tikz-timing/tikz-timing.pdf

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for How to find the ESR of a capacitor

2010-07-16T14:22:32Z

How "low" depends on the efficiency and reliability you are trying to achieve. For low ESR capacitors the manufacturer will supply the values.

Search for Nichicon low ESR capacitors and you will find parts that have a low ESR. The VR series is not a low series resistance capacitor. The PM Series is and the ESR is specified in the datasheet. Nichicon (which makes excellent capacitors) may have some newer series.

The ESR is critical to the life of the capacitor since as ESR increases the temperature of the capacitor will increase which will decrease its life.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Using LCD's of mobiles?

2010-07-13T11:28:39Z

A friend of mine did a teardown of an LCD that he purchased for 0.50USD from Electronic Goldmine -- http://tim.cexx.org/?page_id=342

It is quite detailed so even if you don't use that particular screen you may be able to follow the steps to interface other screens.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for setting up an electronic load

2010-07-13T11:14:03Z

For most testing constant current is the easiest mode to use. You can set the current to the appropriate current level and verify the output voltage specification.

Constant Current -- the load will try to sink the programmed current
Constant Resistance -- the load will try to sink a current to maintain a programmed resistance. This is done my multipliers in the control circuit.
Constant Voltage -- the load will will increase current to maintain a programmed voltage. This is useful when trying to find the current at which the power supply folds back (knee current). You set the load to the foldback voltage and then measure the current. It is quicker than stepping the current but does require a more complex control circuit.

Since most loads are current sinks you shouldn't be able to damage it when the supply is putting out low voltages. You could damage the load with too high a voltage but for an ATX power supply this is unlikely. The output stage of most loads consists of power MOSFETs and these typically have breakdown voltages of 20V and above.

Some power supplies have minimum load requirements for the individual outputs. A comprehensive test would load all the outputs at various combinations of min and max loads but you could probably attach the load to one output at a time. Make sure that each of the other outputs has the min load.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for LED Driver for 300mA LEDs

2010-07-13T00:16:59Z

I have controlled the high current LEDs with both current sources and current sinks.

I am just finishing up the testing on an LT3755 driver circuit (current source) that is driving 12 3W Cree XLamps. This driver has excellent performance if you are careful with the layout. This device can do almost a 10:1 boost at 50W! Being able to simulate in LTSpice was extremely convenient.

If you want a simpler layout you could look at current sinks. You would need to get a supply capable of producing a voltage slightly greater than the sum of the Vf(max) of your LEDs. Using a FET and op-amp you would create a voltage controlled current sink. You could PWM this by setting the current to zero. I use an analog switch on my current-sink.

Here is a picture of my current sink design -- http://wiblocks.luciani.org/not-quite-ready/ZB1-ISINK-index.html The FETs are rated for 40A, the connectors are rated for 10A. For an LED application with a reasonable size heatsink you can probably go to 2A. The LEDs in the pictures are being driven at 350mA. No heatsinking is required if the dissipation in the FETs is kept below 1W.

The board in the picture is being controlled by my Arduino compatible NB1 board.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for What is the best Magnifier to use for general electronics duties...

2010-07-11T23:32:43Z

I use the Luxo 17113, KRM Series, 3 diopter lense on my bench. The combination of the light and magnification is excellent. The Luxo looks similar to the lamp you linked to.

I also use the Bausch & Lomb 81-42-00 visor. It comes with 3 Lenses 1.8x, 2.2x, 2.6x Magnification Power. These were around $40 or so from Amazon. I have a pair on my bench and a pair in the garage. These work quite well but when I work on the bench I only use the lamp + magnifier. The portability of the visor is a major convenience. The multiple lenses is also handy.

I do primarily SMD soldering. My other tool picks are at http://wiblocks.luciani.org/FAQ/faq-tools.html

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Can I Filter This Split Power Supply?

2010-04-21T13:40:35Z

I would use the ICL7660S instead. A couple of benefits --

The S version switches at 35KHz which is above the audio range.
The S version can switch 12V. If you did a +-12V conversion you could do a +-9V linear regulation on the output. This will reduce the noise.

You should be able to add a series inductor and another capacitor on the output. I am assuming you are using ceramic caps (X5R or X7R).

The load regulation of these switched capacitor converters is not that good under load. I am assuming that your synth only needs currents around 20mA or so. Check the specs for the voltage and current limit specs.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for What are the freeware SPICE simulators available?

2009-12-22T00:36:55Z

[I made a couple of additions (* jcl *)]

ngSpice is available for gEDA.
gnuCAP is also available for gEDA.
LTSpice is free from Linear Technology.

I thought that one of the other analog chip makers had a spice too but I can't remember who :(

I have been to a few talks on simulation given by physicists and EEs who have done chip design. Each of the talks seems to end like this ---

Except for simple circuits you will spend most of your getting models and determining where the models need to be modified for your application.
Unless you are doing work for an IC manufacturer the manufacturer will not give you detailed models.
You will not be able to avoid a prototype.
You should only simulate subsections of your design. Simulating the entire design is not usually practical.

Also most of the free simulators are not distributed with models. Re-distribution of the models is usually a copyright violation. LTspice is distributed with models of the Linear Tech parts. I am not sure the quality of the models. Most manufacturers do not want to reveal too many details about their process.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Learning Electrical Engineering

2010-07-09T11:27:20Z

For EE concepts --

Lessons in electric circuits is an excellent free resource -- http://www.openbookproject.net/electricCircuits/

I would also recommend "The Art of Electronics" and the various cookbooks by Don Lancaster.

All of my recommendations are at http://wiblocks.luciani.org/FAQ/faq-books-ee.html

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Do you layout in mil or mm?

2010-07-06T14:04:06Z

Typically I place parts on a 25mil grid and route on a 5mil grid. For low density boards I can usually route on a 10-25mil grid.

When I route I have the traces snap to the mid-point of the pad so that traces end in the center of the pad for all components.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for SICP for Electrical/Electronics Engineers?

2010-07-04T11:20:46Z

I would recommend the The Art of Electronics. Essential reading and is well regarded by EE's at a variety of skill levels. A Physics collection I have found very useful in EE works are the Feynman Lectures. A list of my other book recommendations is at http://wiblocks.luciani.org/FAQ/faq-books-ee.html

(* jcl *)

P.S. SICP is one of my favorites for CS. TAOCP is probably at the top of the list.

The Art of Electronics Author: Horowitz and Hill Publisher: Cambridge University Press; 2nd edition (July 28, 1989) ISBN-10: 0521370957 ISBN-13: 978-0521370950

The Feynman Lectures on Physics (3 Volume Set) Author: Richard Phillips Feynman Publisher: Addison Wesley Longman (June 1970) ISBN-10: 0201021153 ISBN-13: 978-0201021158

Sizing SMD components for Hobbyist Kits

2010-01-26T17:32:59Z

More components are only available in SMD packages. For hobbyist assembly the options are to buy breakout boards or solder SMD.

Since components are usually packaged in a couple of SMD package types I am trying to put together a set of guidelines for choosing packages that are compatible with hobbyist skills and tools. I would consider hobbyist level tools for SMD assembly as -- soldering iron in the $50-$100 range (new), for magnification a $40 visor (like the B&L) and tweezers.

For the kits I make now I use the following guidelines --

Passives 0805 or larger
Min Lead Pitch for SOIC or QFP -- 0.5mm
No QFN, LGA or BGA
Prefered package for gates, BJT, FET --- SOT23
Diodes SOD123 (or larger)

I am interested in recommendations on component selection, minimum tool requirements and assembly issues. Specific tool changes (like solder tip size) that enabled you to do SMD assembly with your existing tools would be useful too.

Thanks.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Adding BT connectivity to Arduino

2010-07-01T01:14:20Z

I have designed a few boards that integrate an Atmel uC (328 and 644) with BlueGiga WT12A. The BlueGiga interfaces to the UART so you send and receive ASCII strings. If you are using a 328 based board you will need to multiplex the UART or use the NewSoftSerial to emulate a UART on the unused pins.

I did the hardware design and the low-level software so I don't know the details of the Bluetooth communication. After I could demo that the uC paired with the phone my portion of the project was complete ;)

Changing the name didn't require firmware changes. I sent a "SET BT NAME" command to change the name to show the device was pairing.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Zigbee products shipped in 2009

2010-07-01T01:04:03Z

You may want to browse around over at http://www.zigbee.org to see if any of the news or press releases mention volumes.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Soldering substitutes?

2010-06-23T23:07:13Z

Wire-wrapping is a substitute for soldering but wire-wrap supplies can get very expensive unless you buy in very large volumes or happen to find a surplus deal.
You could also crimp the wires together. There are terminals called butt splices. You could insert multiple wires into the terminal and then crimp. These are meant for thinner stranded wires but could work for solid leads. Butt splices have two ends but there may be some sort of small ferule you could purchase.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for What are some reasons to connect capacitors in series?

2010-06-17T20:04:40Z

I have only seen it done to increase voltage. On some power supply front-ends (AC/DC conversion) with a voltage doubler the capacitors are in parallel at low voltage and in series at high voltage. This works out well since for a constant power out the current is double at the lower voltage.

As you mention balancing resistors are required.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Switching relay with a PNP and TTL levels

2010-06-10T11:15:44Z

You can't switch the PNP on and off with TTL levels. Since the emitter will be tied to 29V the base needs to be at 29V to turn it off. You need to do a level shift using a second transistor which is either an NPN or an N-channel MOSFET.

Using an NPN transistor the current limiting resistor will then be determined by

R = (29.4 - Vbe1 - Vce2) / Ib1

where Vbe1 and Ib1 are for the PNP transistor and Vce2 is for the NPN tranistor.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for Recommended PCB houses / Assemblers

2010-06-02T16:24:53Z

Assembly can get very expensive unless you are making 1K or more pieces. At 1K pieces the setup costs start to amortize to reasonable values. If you can get to 10K pieces then you could source the parts from China too.

I have had Gold Phoenix and E-Teknet quote on a job. They both had similar quotes. Since I only wanted to do 1K pieces the pricing did not work out and I did not do the project.

Neil Munzinger ( sales@e-teknet.com ) at E-Teknet was very responsive to my questions and made recommendations about cost saving opportunities. Unfortunately the numbers didn't work.

(* jcl *)

http://www.wiblocks.com

Answer by jluciani for CharliePlexing on a breadboard

2010-05-29T19:22:52Z

Take a look at my charlie-plexing schematic at http://wiblocks.luciani.org/FAQ/faq-charlie-plex.html

Make each row connection the common pin of the seven segment readout. Make each column the individual pin connection. For 28 segments you need six pins. If you use eight pins instead of six you may find it easier to program. With eight pins I would do four rows and seven columns.

(* jcl *)

http://www.wiblocks.com

What hobbyist level groups meet to discuss electronics and microcontroller applications?

2010-05-26T14:19:26Z

What hobbyist level groups meet to discuss electronics and microcontroller applications? I am interested in groups that have free and open meetings and meet on a regular basis (typically once per month).

The two I know of in Boston are --

dorkbot Boston -- http://groups.google.com/group/DorkbotBoston?hl=en&pli=1

Boston Arduino Users Group http://www.meetup.com/The-Boston-Arduino-Users-Group

(* jcl *)

Answer by jluciani for What may cause a perfboard to bend ?

2010-05-27T17:34:49Z

It could also be the way you had the board clamped when you soldered the components. If the board had a bend when it was clamped it may not be able to "spring back" after the components are soldered. Not clamping the board could also cause the problem.

What type of board are you using? If you are using epoxy-paper I would switch to epoxy-glass. It should spring back a lot better. It also is less likely to crack and break. I like Vector 169P84WE. The parts I use for breadboarding are listed at the bottom of http://wiblocks.luciani.org/FAQ/faq-tools.html

(* jcl *)

http://www.wiblocks.com

Comment by jluciani

2010-08-01T01:37:28Z

I use my own LaTeX macros for the style. I use METAPOST for some of the diagrams and pdfinclude to embed the shematics, datasheets, etc. The BOMs are done using Postgres. The chip I added is a 12bit DAC not an ADC. Future boards will add higher resolution ADCs. I was thinking of adding the li-ion charger to that question but it seemed like that user was looking for an arduino shield.

Comment by jluciani

2010-07-23T21:40:27Z

I do this too. I will script the generation of these types of documents using Perl + TeX + METAPOST (or other command line tools). When the data changes I type "make" and the changes propagate through.

Comment by jluciani

2010-07-11T23:58:41Z

The Luxo is well built and the optics are very good (and replaceable). it is a professional level tool. Until now I have never seen the ones at Walmart so I am not sure how they compare. MSC direct also sells some lower cost lamps (and IIRC Luxo). Their sales prices can be very good. Just as I was starting to do more SMD soldering I found the Luxo in a clearance bin at Charrette. IIRC it was around $120 or so. Well worth the money.

Comment by jluciani

2010-07-11T23:34:16Z

Why do you prefer the square versus the round?

Comment by jluciani

2010-07-08T11:44:04Z

I am one of the organizers of the local Arduino/Robotics group. All are welcome and I am trying to get more college students involved. We have been meeting monthly at Microsoft NERD which is a few blocks from MIT. Search for us on meetup. Sprout (Somerville) has some project nights and meet-ups. thesprouts.org There is a Boston dorkbot as well. Since dorkbot is based on "doing strange things with electricity" sometimes it's engineering and sometimes art. There is a mailing list for dorkbot. The mailing list may be a good place to ask about other groups as well.

Comment by jluciani

2010-07-01T11:50:15Z

That's surprising since the marketing types usually don't stop talking about those numbers ;) Send them an email. Someone from sales will send you the information (especially if they think you are interested in a license ;)

Comment by jluciani

2010-06-25T15:13:50Z

joeforker's comment about obsolete components applies to other parts like semiconductors. The type of components you want depends on the types of projects you are doing. Lot's of systems in the past had a triple power supply (+5V, +-15V). Newer designs are going to single supplies. If you had a lot of dual supply op-amps (like the LM741) it may not meet your future needs. I would put the LM741 on the NO list. I would add some ceramic caps to the list but not to many since the recent improvements in dielectric have pushed the size and the cost down.

Comment by jluciani

2010-06-20T20:33:04Z

Have you used them for assembly or just PCB fab?

Comment by jluciani

2010-06-16T02:30:26Z

That's the one. Sorry about the misspelling. Since March I have used the pod quite a bit to debug a uSD library. The device is worth the money but the software interface is awkward. I am not sure if other devices in the price range are any better. If I used this tool a lot I would look into writing my own interface.

Comment by jluciani

2010-06-04T13:57:00Z

Glad you liked it. At the last Ignite I received a free copy. I have done a couple of the first projects with my seven year old.

Comment by jluciani

2010-05-28T17:07:51Z

If the board is dense you could also turn existing vias into programming points. You need to remove the soldermask and possibly change the pad and hole size. A row of pads could be a lot easier if it fits.

Comment by jluciani

2010-05-27T22:14:16Z

They kind of look like epoxy-paper. If you can hold the board flat with a vice or clamp while you solder it may bend less when the clamp is removed.

Comment by jluciani

2010-05-12T02:13:31Z

Thankss (* jcl *)

Comment by jluciani

2010-05-04T21:12:49Z

Since it is an assortment from eBAY it may not be a mfg pn. It could be some sort of OEM number.

Comment by jluciani

2010-05-04T21:08:07Z

Are you pressing the reset button on the Arduino immediately before you download?