Curiously Strong Power Supply Design

18VAC dual secondary 160VA toroid into a full wave rectifier with 32*470uF caps, for about 5.5Vpp ripple at 10A. Rectified output is fed into four MC34063 based SMPS supplies, three step-down and one inverting. The outputs of the SMPS are fed into 5 linear regulators, for a 15V bipolar rails, 15V power amp rail, 10V small amp rail, and 6V shifty VU rail. Designs are compatible with non through hole plate boards. All boards will be fabricated on a Taig 2019CR CNC mill.

cs_regulators_schema.png

Posted by rmrubin Posted in: Make2008, Electronics Comments Off April 2008

ATTiny44 Based Shifty VU Meter Controller (MAKE2008)

Schematic and circuit board design for the Shifty VU Controller. Designed for an Altoids tin chassis, the analog section includes a stereo full-wave rectifier made with a quad rail-to-rail opamp, with logic FET switched capacitors to adjust the rectifier output’s rolloff delay.

shifty_vu_controller_schema.png

Posted by rmrubin Posted in: Make2008, Electronics Comments Off April 2008

Curiously Strong TriAmp Speaker Selection

Tang Band drivers from Parts Express. 300Hz and 5KHz look good for crossover. $2 Goldwood tweeters. Not worth posting (even if they did have specs, which they don’t). Chassis is planned to be laser cut acrylic (!) courtesy of macetech and Techshop. A high density cardboard concrete/plaster casting tube may be integrated into the design as a waveguide for the 5″ driver. Open Baffle mid drivers are also being considered.

Posted by rmrubin Posted in: Make2008, Electronics Comments Off April 2008

Grow LED Array Rev.2 Results AKA Why Rev.3

Why Rev.3?
- Topside ground plane connection underneath connector. Inaccessible, non functional without thru-hole plating without wire cludge.
- White rail dissipation in PNP pass transistors very far beyond spec. Red rail to spec only below 25C ambient.
- Transition to ethernet input.

 

 

Short term testing of hardware observations:
- Normal room temp.
- 25V unregulated psu.
- All circuits function as intended.
- Red and blue series transistors warm to touch.
- White series transistor hot set at 1/2 normal current.

Conclusions:
- Multiple rail PSU, <0.8V overhead at max string Vf. Blue rail is an example. Benefit is less dissipation per output.
- SOT223 instead of SOT23 3906 series transistors. Same dissipation but within spec. Benefit is single-rail lower-cost psu and a sexier transistor package.
- Dropping resistors for white and red LED rails. electrically same as SOT223 dissipation, retain cheaper SOT23 package.
- Higher dissipation SOT23 PNP for red rail viability without resistor. Must test at higher ambient.(MMBT4403?)
- Three channels current feedback SMPS. Much less dissipation, psu same level complication as tri rail. Cost benefit unknown.

Paper Test:

LED Vf(max)
Red =2.4
Blue =3.6
White =3.6

LED Vf(typ)
Red =1.7
Blue =2.8
White =2.8

String Vf(max)
8x Red =19.2
6x Blue =21.6
2x White =7.2

String Vf(typ)
8x Red =13.6
6x Blue =16.8
2x White =5.6

String W(max) @ 20mA
8x Red =0.384
6x Blue =0.432
2x White =0.114

String W(typ) @ 20mA
8x Red =0.272
6x Blue =0.336
2x White =0.112

System Output W(max) @ 20mA
4x Red Strings =1.536
3x Blue Strings =1.296
1x White Strings =0.228
RB Total =2.832
RBW Total =3.060

System Output W(typ) @ 20mA
4x Red Strings =1.088
3x Blue Strings =1.008
1x White Strings =0.288
RB Total =2.096
RBW Total =2.384

MMBT3904 Vce(max) @ 23V V[supply]-Vf[string_max]-Vbe[0.6V]
Red =3.2
Blue =0.8
White =15.2

MMBT3904 Vce(typ) @ 23V V[supply]-Vf[string_typ]-Vbe[0.6V]
Red =8.8
Blue =5.6
White =16.8

MMBT3904 mW(max) @ 23V/20mA
Red =64
Blue =16
White =304

MMBT3904 mW(typ) @ 23V/20mA
Red =176
Blue =112
White =336

MMBT2904 Temp(max) @ 23V/20mA 357C/W
Red =22.848
Blue =5.712
White =108.528

MMBT3904 Temp(typ) @ 23V/20mA 357C/W
Red =62.832
Blue =39.984
White =119.952

MMBT3904 mW_derate(max) 23V/20mA Ambient 25C 2.8mW/C
Red =63.9744
Blue =15.9936
White =303.8784

MMBT3904 mW_derate(typ) 23V/20mA Ambient 25C 2.8mW/C
Red =175.9296
Blue =111.9552
White =335.8656

MMBT3906 mW_overhead(max) 23V/20mA/25C 350mW[SOT23]-mW_derating-mW_used
Red =223
Blue =319
White =-257(!)

MMBT3906 mW_overhead(typ) 23V/20mA/25C 350mW SOT23
Red =-1
Blue =127
White =-321(!)

MMBT3906 Source, Vf(max)/If=20mA/23V/25C/77F
Red = OK
Blue = OK
White = FAIL

MMBT3906 Source, Vf(typ)/If=20mA/23V/25C/77F
Red = ALMOST, BUT FAILED
Blue = OK
White = FAIL

Posted by rmrubin Posted in: Electronics Comments Off April 2008

Grow LED Array Prototype Rev. 2

Button pinouts were mirrored. Both switch channels of the button were used in order to reduce single element through current. Single-sided routing was dropped in order to pass DRC at 20mil. No benefits of single sided besides challenge, as most fab houses do not seem to care. The higher resolution boards were difficult to toner etch properly with my level of skill. The lower resolution will allow for easier etching and milling with tools at hand. A pair of arrays will be made in each method, in order to compare milled and etched PCB technologies. Some LED pins must be soldered top side due to lack of through hole plating.

Posted by rmrubin Posted in: Electronics Comments Off March 2008

MAKE 2008 Grow LEDs Array Prototype Design

Single sided board design for an array of 24 blue, 24 red, and 2 white LED. For use as small plant lighting. Switching (SMPS) power supply and optional digital control unit are external, and support a minimum of 2 arrays. The white LED are switched with a latching button. Series strings of LED are brightness regulated using MMBT3906 based current sources for immunity to poorly matched Vf and variable supply voltages, 8 blue LED and 6 red LED per string. This setup will be powered by 24V rails, to provide headroom for the LED strings at Vf(max) and and 1V needed by the current regulators. A control unit will modulate power with PWM switching at greater than 200Hz, and be capable of simulating day/night cycles, movement of the sun from horizon to horizon, and adjusting the red and blue light balance.

Posted by rmrubin Posted in: Electronics Comments Off March 2008

Stereo Audio IO Landing Pad for Olimex SAM7-H256: Assembled

CNC milled dual channel audio input/output board for the Olimex SAM7-h256 and SAM7-H64 header boards. Input is through an AC-coupled preamp with a single-pole bandpass input with attenuation into a rail to rail opamp in voltage follower configuration. -3db response was simulated at 2Hz-30KHz. A though port is provided to use the device an an audio monitor. Output is a pair of SAM7 PWM through a 4-pole active low-pass filter. Configuration is butterworth salen-key at 10KHz. High end audio hurts. The LED VU display is unbuffered, running at about 2.4 mA, about half a mA beyond spec for 4 of those pins. Headers are provided for asynchronous RS232 comm and external 3.3V supply. Currently it gets power from the USB.

• dts7had01_schema.png
• dts7had01_parts.txt

Posted by rmrubin Posted in: Electronics Comments Off February 2008

Jabra BT125 Bluetooth Headset Teardown

Two very small torx screws, edge snaps, some plastic hooks at the end with mating feature on the opposite chassis piece. Speaker is insulated from the main chassis by a rubber-like pad. The mic is built into a pod made of the same rubbery material, which when mounted fits flush with the outer chassis. Torx screws came out with a clipped xacto blade tip.

Going to swap the blue 0603 LED for a red one. Maybe amber. Will possibly swap the 0402 resistor with a larger one. Try to kill the sniper beacon blink effect. Alternative is a thick film or thin paper light filter behind the translucent white button.

The grid is .250″.

Posted by rmrubin Posted in: Electronics Comments Off February 2008

ASUS Tech Support Confirms Two Year Hardware Warranty Details. I’m Getting 2GB.

Today I contacted ASUS Notebook Support (510-739-3777 Ext. 5110) twice in order to confirm the details of my Eee PC 4G warranty. I talked to James the first time, and Clinton the second time. Both were very helpful and quick with the information needed to answer my questions.  I was only asked for the serial number on my Eee PC. This is what I learned:

• 2 Year Hardware Warranty
• 6 Month Battery Warranty
• ASUS is not responsible for for software misconfiguration, such as troubleshooting an alternative operating system.
• ASUS Support will help you restore your Eee PC to its default Xanadros Linux state.
• Installing 2GB SO-DIMM will not void your warranty.
• Operating system and program disc writes, referred to by ASUS Support as “normal computer usage,” does not void your warranty. This means using swap, pagefiles, persistent system logs, programs that do heavy disc writes, and modern journaling filesystems like NTFS, ext3, and reiserfs will not void your Eee PC’s hardware warranty.

It was noted by ASUS Support that in the event of an SSD failure, they would have a difficult time actually finding the cause of the failure. In many cases it would be impossible. Also, in the case of 2GB RAM installation, you would return your Eee PC to ASUS with the original RAM SODIMM. ASUS Support, regarding the 2GB SODIMM: “We would ask you to send the Eee PC back like it originally came.”

I honestly think it’s insane to run a non-journaling filesystems on a laptop. The technology was developed to deal with precisely the type of situations a filesystem on a laptop will encounter, and both Microsoft and GNU/Linux builders have adopted journaling filesystems for primary storage use. If your SSD burns out because of heavy disc writes or first generation manufacturing defects, ASUS Support says they will take care of you.

Posted by rmrubin Posted in: Eee PC Comments Off January 2008

Booting An ISOLINUX LiveCD From Eee PC’s SD Card Reader

This is a simple method to boot an ISOLINUX-based LiveCD from the SD card reader of the Asus Eee PC small-footprint notebook computer. It can be used to boot Linux LiveCDs or installation CDs based on the ISOLINUX CDROM bootloader. It is non-destructive, and will work if files already exist on the SD card. Demonstration is from a WinXP/Cygwin environment with a SYSLINUX Windows binary package, but it should work from a GNU/Linux system as SYSLINUX is available for both platforms. This method should work for computers besides the Eee PC and with other types of usb storage media, such as memory sticks, CF cards, and hard drives.

This method is recommended over the usb booting method described on disc 2 of the Slackware 12 Installation CD. With the boot method described here you can use the SD as a normal storage device. You do not have use a separate storage medium for the package sets, or do a net-based installation, because you can store the package sets on the SD card itself. Also, you wont have to wait for the 23MB usbboot.s image to load.

Tested on Eee PC 4G:

• eeeXubuntu LiveCD - Boots to desktop. No further testing.
• SystemRescueCD LiveCD - Normal functionality. Includes cfdisk for nLite pre-install.
• Damn Small Linux LiveCD - Boots to desktop. No further testing.
• Slackware 12 Install CD - Normal functionality. Mount SD and specify package set dir.
• Gentoo Minimal Install CD - System init failure after kernel init. Sadness.

Needed:

• SD card with enough capacity for your LiveCD image files.
• PC to format and copy files from an .iso image to an SD card.
• SYSLINUX package for your operating system.
• Your Eee PC.

Overview:

• Format the SD card.
• Copy files from ISOLINUX LiveCD image to SD.
• Adjust the ISOLINUX files for use with SYSLINUX.
• Make the SD bootable with SYSLINUX.
• Boot from SD on the Eee PC.

Step 1: Format the SD card.

Insert the SD card into your PC and wait for the hardware to be detected. If you want to start with a clean SD card, you should format it now. In Windows, you do this by right-clicking the drive in the My Computers window and selecting “Format…”. Select FAT or FAT32 filesystem, and check Quick Format to save time and lengthen SD life. The card will be made bootable later with SYSLINUX. In Linux you would use mkdosfs and it would also be a good time to use a program like cfdisk to make the SD partition bootable. Please note that most SD cards come pre-formatted, and this method is non-destructive. It does not require you to format the card at all if its capacity is adequate.

Step 2: Copy files from ISOLINUX LiveCD image to SD.

All files must be copied from the .iso LiveCD image to the root of the formatted SD card. In Windows, you can use a program like 7-Zip to open the .iso image like an archive, or Daemon Tools to mount the .iso as an emulated CDROM drive. In Linux you would use the command “mount -t iso9660 -o loop /path/file.iso /mnt/dir” to mount the image onto a directory. You will also need to mount the SD card device: “mount -t auto /dev/sdx1 /mnt/dir”. Once you have copied all files from the .iso CD image onto the SD card you can delete the CD image. In Linux you should unmount the image first.

Step 3: Adjust the ISOLINUX files for use with SYSLINUX.

Find the “isolinux” directory on the SD drive. It might be in another location besides the root directory, such as “/boot”. When you locate it, copy all files from the “isolinux” directory to the root directory of the SD card. Rename the file “isolinux.cfg” to “syslinux.cfg”. You should not need to edit the file. If you are running Linux, you can unmount the SD card now. You should have made the SD card bootable with a program like cfdisk by now.

Step 4: Make the SD bootable with SYSLINUX.

Download the SYSLINUX package for your operating system. If you are using Linux, check your distribution package sets for a SYSLINUX build or read the available build and installation documentation. In Windows, simply download the binary package and unzip. The following was done in Windows on a Cygwin/bash shell, however it should be very similar in Linux:

$ cd /d/software/free/system/syslinux/syslinux-3.60/win32/

$ ./syslinux.exe -a g:

Do not use the “-s” option, as specified in other SYSLINUX for usb examples. It installs SYSLINUX in a slow/safe mode that can make booting take a very long time, and is not needed for booting from the Eee PC SD card reader. Be aware that the “-a” option to make the partition bootable is not available in the Linux version. This is why you must use a program like cfdisk to make the partition bootable before attempting to boot from the SD card.

Step 5: Boot from SD on the Eee PC.

If the Eee PC was on, shut it down. Remove the prepared SD card from the PC and insert it into the Eee PC’s card reader. Press the power button to start the Eee PC, and tap the Esc key a few times during the POST screen to load the boot device selection menu. Select “USB:USB2.0 CardReader SD0″ and hit Enter. This should load the ISOLINUX system from your SD card. Note that although some kernels may boot and initialize correctly, the host system may not detect your hardware correctly and may fail trying to find files on the SD. If the system was setup to boot from a framebuffer VGA console, the kernel will immediately present you with a message asking you what screen mode you would like to use. They range from 80×25 to 80×60 characters resolution. You must specify the screen mode with a hex value. My suggestion is using F02, or 80×43 characters VGA console resolution.

Posted by rmrubin Posted in: Eee PC Comments Off January 2008

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