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

Tri-Rail SMPS VFD Clock PSU Schematic

Not posted previously. Laziness.

Posted by rmrubin Posted in: Electronics Comments Off January 2008

Atmel AT91SAM7S, ARM7TMDI, OpenOCD and Olimex SAM7-H256 Doc Compilation

A document compilation for a recent purchase of an Olimex SAM7-H256 from SparkFun, an Atmel AT91SAM7S256 based breakout-header dev-board. Includes relevent manuals, datasheets, application notes, and example files from Atmel, ARM, the OpenOCD project, and board descriptions of the Olimex header board.

bzip2 compression was used to decrease file size from 100MB+ to only 35MB.

at91sam7s_docs_all.tar.bz2

Posted by rmrubin Posted in: Programming, Electronics Comments Off December 2007

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