EEVblog #735 - Mailbag

[EEVblog]

Another movie length Mailbag.
What have people sent in this week?

SPOILERS:
Why are cheap Ebay LED light bulbs so bad? Dave investigates why some of them are doomed to fail. DaveCAD and thermal camera time.
http://www.qt-brightek.com/datasheet/QBLP679E-IWK-XX.pdf

CPM700 Countersurveillance unit from Research Electronics Inc for cold war spy bug sweeping.

Raspberry Pi I/O Hat Kickstarter, the Hatilogico:
https://www.kickstarter.com/projects/jelby/hatalogico-for-the-raspberry-pi

Industrial RS232 modem teardown

Bricked Assus TF300 Transformer Tablet

Annoy-a-tron

Belkin router teardown

Cypress Parachute Automatic Activation Device.
Previous video teardown on this:

[int2str]

Bluetooth radio is CSR - Cambridge Sillicon Radio (http://csr.com/).
One of the 3-4 major BT chip makers.

 

[Artlav]

Nitpicking mood...

-When i was skydiving, the parachute opener pulled the main chute after a pre-set freefall duration. The reserve chute is a completely separate unit. But i was using paratrooper hardware, sports gear might be different.

-I wanted to say that shouldn't the tablet/transformer have a regular usb charge input on itself, you just don't charge it with keyboard attached, so no one cares about that weird connector. But unfortunately, nope. They are evil.

-The tablet should be openable - it's a basically a plastic back clipped onto a screen&electronics part. Give or take a couple screws at the edges.

-The resistor in the router was on a pad marked L1, so most likely not in place of a current sense resistor.

[NF6X]

That calculator isn't just a 4-banger... it's an RPN 4-banger! It may seem like a small heap of crap today, but when it was introduced in 1974, I think it was one of the earliest calculators using chip-on-board assembly, and it just cost $17. My first calculator as a boy was the same one, but re-branded as the Montgomery Ward P10.

Pictures here: http://spyropoulos.net/calcs-other/calcs-rpn.htm

I don't think I still have my original one, unfortunately. I was probably around 5 or 6 years old when my dad bought it for me. I didn't understand the significance at the time, but it was an RPN calculator just like Dad's vastly more expensive HP calculator from work.

[kc9qvl]

The real evil thing about that Asus Transformer is not the proprietary plug but that the tablet charges at 15vdc through that usb cable thing. You don't want to accidentally use the 15v wall wart to charge a 5v phone.

[NiHaoMike]

The real evil thing about that Asus Transformer is not the proprietary plug but that the tablet charges at 15vdc through that usb cable thing. You don't want to accidentally use the 15v wall wart to charge a 5v phone.

The HVDCP will not operate at 15V unless it detects a pullup on the USB 3 ground.

[jfasoc]

The CYPRES is connected to the reserve parachute. It will open the parachute at about 225m above the ground. When in free fall you normally fall with at least 50m/s (I have been measured at 98m/s in a head down). That means the reserve is deployed less that 4 seconds before you find out that it is the ground that is the limit.

[Zbig]

Is it only me who thinks the "Warranty void if open" was a joke prepared by sender, which Dave failed to play along, and the envelope actually contained a note?

[DanielS]

If the LED lamps were run off 12V AC, the drop resistors would heat up a fair bit more with around 8V across them at peak instead of 2V.

If I did my math right, I get 475mW per resistor.

[PA0PBZ]

A sneak preview of the cpm700 guts:

[kc9qvl]

The real evil thing about that Asus Transformer is not the proprietary plug but that the tablet charges at 15vdc through that usb cable thing. You don't want to accidentally use the 15v wall wart to charge a 5v phone.

The HVDCP will not operate at 15V unless it detects a pullup on the USB 3 ground.

Well yeah if it works correctly.

[FivePoint0]

I'm not all convinced with the explanations offered for the failure of the LED bulb.  SMD resistors will run at rated power up to 70°C (although I never do it) and so will "cheap" FR4.

I'd bet the LEDs would last forever on your nice regulated bench supply.

What if the actual supply that toasted the LEDs was designed for higher power output like what would be needed for tungsten bulbs of say 20W+.  It might be rated at 12V under load.  Who knows what voltage is given out under light loads like presented by the LEDs.

If the supply increases to only 14V what happens to the resistor dissipation?  Are they fried?

This design appears to assume use of a stable supply voltage.  I would have to put less LEDs in series along with a larger current limit resistor that way changes in supply voltage have less effect on current draw.  It's is less efficient, granted.  A little switcher would be nice.

I've not done the math but I didn't like to see the chips connected in parallel, how does Vf vary with temperature?!.  There was plenty of space on the rear of the board for more resistors, and lots of spread out SMD resistors can give a good power dissipation.

Could I do better? Yes.  Would it cost more.  Yes.

[jolshefsky]

I'm not all convinced with the explanations offered for the failure of the LED bulb.  SMD resistors will run at rated power up to 70°C (although I never do it) and so will "cheap" FR4.

I'd bet the LEDs would last forever on your nice regulated bench supply.

I think the issue is less that the components are outside their ratings, it's that they are pretty close for open air. These look like they're designed to replace incandescent/halogen bulbs inside enclosures, and when you're marginal in open air, you're hopeless in any kind of enclosure. At around 10 watts draw, I bet leaving it turned on under a sheet of paper would cause it to fail in tens of hours.

[ThisDoesNotCompute]

Dave, any chance we could get a scan/PDF of the countersurveillance unit's manual? Looks like interesting reading!

[boffin]

Dave, any chance we could get a scan/PDF of the countersurveillance unit's manual? Looks like interesting reading!

PDFs from the manufacturer:
http://www.reiusa.net/system/products/CPM-700/CPM_700_Deluxe.pdf
http://www.research-electronics.com/system/products/CPM-700/CPM%20Manual-web.pdf

[bitwelder]

Does that Asus custom evil connector have only USB / power pins or is there an even more custom cable that bring out of the Transformer some other internal port?

[Fungus]

I'm not all convinced with the explanations offered for the failure of the LED bulb.  SMD resistors will run at rated power up to 70°C (although I never do it) and so will "cheap" FR4.

Sure, but Dave measured them at 70C in free air.

Put them in a small enclosed space and they're going to get much hotter than that.

[electr_peter]

I think that POS LED unit is an excellent example of very high thermal resistivity. Sure, components will work well in 70C or low 100C environment and total power is relatively low, but that small power add ups and ups till everything is cooked.

Analogy would be an empty plugged bath with slowly dripping/running shower head. Power (amount of water) is small, but it has nowhere to go and eventually could fill all bath (or cook LED PCB till it is a toast).

Sad things is, many cheap energy saving lamps (LED and fluorescent) will die prematurely because of overheating. Typical lamp enclosure is a closed box with no ventilation at the top, only entry hole in the bottom. Some newer lamps has enclosures designed to act as a heatsinks (taking heat with metal structures and heat flow though top holes).

[NiHaoMike]

Does that Asus custom evil connector have only USB / power pins or is there an even more custom cable that bring out of the Transformer some other internal port?

It also has I2C for the keyboard, a connection to the keyboard battery, HSIC to a HSIC-USB bridge inside the keyboard, and a few other signals. Quite a complex design.

BTW, I added a boost converter to mine to allow it to (slowly) charge from USB, added a little more battery capacity, and also brought out two more USB ports from the HSIC-USB bridge, one brought out to the outside and the other left in place for a future upgrade. It's very surprising just how much room there is in the keyboard. In the tablet itself, I replaced the stock Wifi antenna with a patch antenna.

[Fungus]

Does that Asus custom evil connector have only USB / power pins or is there an even more custom cable that bring out of the Transformer some other internal port?

It also has I2C for the keyboard, a connection to the keyboard battery, HSIC to a HSIC-USB bridge inside the keyboard, and a few other signals. Quite a complex design.

I thought that too - it need more wires for the keyboard!

And then I thought: But ... if it was a USB connector for charging the keyboard could be a USB keyboard. That's what USB is for! Universal Serial Bus.

So yeah, there's no excuse.

[velin]

I also think that the 12V AC power is the reason for burning the LED's. AC is the common power source for this type of lamps, which this LED is designed to replace. With AC, resistors and LED's will be definitely overloaded!
I had this problem with my own LED lamps

[broderp]

I have that ASUS tablet and keyboard combo.  Love it. 

What Dave doesn't get is that this tablet charges on 15VDC.  NOT 5VDC. 

This thing charges to full in about an hour and the charge lasts for hours. 

It runs rings around other Samsung or Apple tablets friends and family have when it comes to charging.   

It also has Tegra video. 

The tradeoff is justified IMO for the function and performance.  I travel with mine in place of a regular laptop.

Just my two cents worth...

Love mailbag..

[NiHaoMike]

It also has I2C for the keyboard, a connection to the keyboard battery, HSIC to a HSIC-USB bridge inside the keyboard, and a few other signals. Quite a complex design.

I thought that too - it need more wires for the keyboard!

And then I thought: But ... if it was a USB connector for charging the keyboard could be a USB keyboard. That's what USB is for! Universal Serial Bus.

So yeah, there's no excuse.

I2C is much lower power than USB. It's especially significant on a mobile device.

[miguelvp]

I still use my TF-201 (transformer) everyday, even to read this forum.

Last I used it was while flying back from Boston to Chicago using the Airplane's WiFi.



I started with the battery not fully charged because I was using the tablet (netbook or whatever) at Logan International in Boston, so the built in battery in the keyboard had plenty of charge left even after getting home.

The powerbrick is 15V as others have mentioned and replacements are easy to find on ebay, I did purchase one because I wanted a 2nd data cable.

You can also plug a hub on the usb and put ethernet, keyboard & mouse. OS on mine is Android ICS, the Nvidia chip is a Tegra 3, old tech by todays standards but powerful enough for some decent 3d graphic games.

Browser is not the speediest compared to the Tegra 4 on the now old Nvidia Shield, or the superfast Tegra K1 that is on the new Shield tablet and other mobile devices. Graphics tripled from Tegra 3 to Tegra 4 and again from Tegra 4 to Tegra K1, maybe even quadrupple.

The Tegra 3 is based on the Arm Cortex-A9 and it's a quad core with an extra low power core, so it's a 4+1 cores as they call it.

[fsanches]

"Cody Wilson" is the name of that guy behind 3d-printed hand guns...