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Project:SpeedAdjustableBikeLight: Difference between revisions

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Project:SpeedAdjustableBikeLight (view source)

Revision as of 02:24, 5 May 2012

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* drilled and milled the LED lense mounts.
* drilled and milled the LED lense mounts.
* purchased parts from DigiKey
* purchased parts from DigiKey
* made schema [http://wiki.london.hackspace.org.uk/w/images/f/f1/Bikelight_09_s.png]
** LT3008ETS8-2.5#TRMPBFCT-ND | 1 | 2.19 | 2.5V Voltage regulator
* two bard layouts, I havnt worked out how to print them yet.
** DFLS130LDICT-ND | 7 | 0.252 | 30V | 1A Schottky Diode
** 568-7420-1-ND | 4 | 0.32 | MOSFET N-CH 30V 4.9A 6TSOP
** MMSZ4680T1GOSCT-ND | 1 | 0.19 | DIODE ZENER 2.2V 500MW SOD-123
** SMBJ5361B-TPMSCT-ND | 2 | 0.63 | DIODE ZENER 5W 27V SMB
** 445-1386-1-ND | 1 0.17 | CAP CER 4.7UF 10V 10% X5R 1206
** PDV-P5001-ND 1 | 1.3 | PHOTOCELL 8K-16K OHM 11MM
** 311-10.0KFRCT-ND | 10 | 0.01 | RES 10.0K OHM 1/4W 1% 1206 SMD
** 311-825FRCT-ND | 1 | 0.02 | RES 825 OHM 1/4W 1% 1206 SMD
* made [http://wiki.london.hackspace.org.uk/w/images/f/f1/Bikelight_09_s.png schema]
* two board layouts, I havnt worked out how to print them yet.


==Thiking progress==
==Thiking progress==
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Start software development... the easy bit.
Start software development... the easy bit.
==Indicator LED==
(distraction)
I picked a 2mA red LED (should preserve night vision and show up well during the day) from Farnells catalog.
* [http://uk.farnell.com/vishay/vlms30k1l2-gs08/led-plcc2-red/dp/1328349 18mcd, 60degree, SMD LED] looks fancy in the jpg and is cheap - £0.51 for 5.




==Switches for LED current==
==Switches for LED current==
* This [http://uk.farnell.com/diodes-inc/zxms6005dt8ta/mosfet-nn-ch-w-esd-60v-1-8a-sm8/dp/1902497 SMD Dual Logic Level MOSFET] will control two sets of LEDs directly from the MCU - given enough heat-sink capability on the board and enough voltage from the MCU (3.3 or 5v compatibke , Has ESD, over temp and over current protection... is really tiny! If the logic level REALLY needs to be 3.3v then that is an issue :( 3.3v logic turns into about +3.45v regulator (3.3v + a 200mV diode drop to allow the MCU tp be reprogramed in circuit) with 415mV regulation margin - nearly 4v reqd for the MCU.. when the LEDs start to light up near 3v :(.
* This [http://uk.farnell.com/stmicroelectronics/stp16nf06l/mosfet-n-ch-60v-16a-to220/dp/9803068 TO220 MOSFET] should carry the 0.5a curent - perhaps without any heatsinking at all. and combined with a small transister should operate well at a supply voltage of 3v.


* This [http://uk.farnell.com/nxp/pmn34un-135/mosfet-n-ch-30v-4-9a-sot457/dp/1758106 PNM34UN] is 2A mosfet, with Rds of 0.08 at 1.8V throu to about 0.05 at 4.5V; max Vds of 30V; £0.16 each. there are several similar parts at Vds 30V for a bit more money. [http://www.digikey.co.uk/product-detail/en/PMN34UN,135/568-7420-1-ND/2698079 digikey ] is more expensive for this part.
* This [http://uk.farnell.com/nxp/pmn34un-135/mosfet-n-ch-30v-4-9a-sot457/dp/1758106 PNM34UN] is 2A mosfet, with Rds of 0.08 at 1.8V throu to about 0.05 at 4.5V; max Vds of 30V; £0.16 each. there are several similar parts at Vds 30V for a bit more money. [http://www.digikey.co.uk/product-detail/en/PMN34UN,135/568-7420-1-ND/2698079 digikey ] is more expensive for this part.
* [http://uk.farnell.com/nxp/pmn27un-135/mosfet-n-ch-20v-5-7a-sot457/dp/1758104 PMN27UN] is similiar to the above; but 20V max Vds with a bit smaller Rds(on) - also marginally cheaper.
There are a few impacts of this choice..
* SMD or through hole!!!
* Many fewer devices from the SMD integrated logic level MOSFETS
* Higher operating voltages might be required by the SMD MOSFETs


==Voltage regulator for the MCU==
==Voltage regulator for the MCU==
Needs to operate of a widely varied supply voltage. The dynamo generates a voltage proportional to the bike speed. Potentially reaching hundreds of volts. And the higher the voltage climbs, the more power I can use in the LEDs! Many components to deal with 0.5A are specced at about 40 to 60V - so that is a very high limit for the working voltage. A chain of 6 LEDs would need 24v. My plans are for 3 LEDs in a chain - so 20V is a good target.
Needs to operate of a widely varied supply voltage. The dynamo generates a voltage proportional to the bike speed. Potentially reaching hundreds of volts. And the higher the voltage climbs, the more power I can use in the LEDs! Many components to deal with 0.5A are specced at about 40 to 60V - so that is a very high limit for the working voltage. A chain of 6 LEDs would need 24v. My plans are for 3 LEDs in a chain - so 20V is a good target.
==voltage regulator==
==digikey options..==


* [http://www.digikey.co.uk/product-detail/en/LT3008ETS8-2.5%23TRMPBF/LT3008ETS8-2.5%23TRMPBFTR-ND/2074413 LT3008 2.5V fixed] from Digi-Key. Is easier to check for alignment on board. Doesn't need the resister network. And is cheaper.
* [http://www.digikey.co.uk/product-detail/en/LT3008ETS8-2.5%23TRMPBF/LT3008ETS8-2.5%23TRMPBFTR-ND/2074413 LT3008 2.5V fixed] from Digi-Key. Is easier to check for alignment on board. Doesn't need the resister network. And is cheaper.
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This diode should allow be low voltage drop - to get the LEDs working at lower speeds.
This diode should allow be low voltage drop - to get the LEDs working at lower speeds.
Need to be >10V barrier. Higher barrier gives higher drops. So chosen 15V barrier diode.
Need to be >10V barrier. Higher barrier gives higher drops. So chosen 15V barrier diode.
* [http://uk.farnell.com/vishay-formerly-i-r/10bq015trpbf/schottky-rectifier-1a/dp/1651136 1A, 360mV fwd voltage drop]


* [http://www.digikey.co.uk/product-detail/en/DFLS130L-7/DFLS130LDICT-ND/673203 digikey 1A 30V 0.31 voltage drop] £0.38/1 £3/10
* [http://www.digikey.co.uk/product-detail/en/DFLS130L-7/DFLS130LDICT-ND/673203 digikey 1A 30V 0.31 voltage drop] £0.38/1 £3/10
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== 20V, 30V or 60V diode bridge. ==
== 20V, 30V or 60V diode bridge. ==


From what I read yesterday, the voltage drop of a schottky diode is a function of the junction temp, the current passed, the reverse voltage barrier, and the size of the diode junction (which I guess becomes cost).
Since the voltage out of the dynamo is essentially a function of the road speed, it could be quite high.  
There is this [http://uk.farnell.com/vishay-formerly-i-r/vs-95sq015/diode-schottky-9a-15v/dp/506795 £3.19 diode 9A/15V] that has a Vf for 1A at 25C less than 250mV. If you could heat the junction to 100C it would be about .1V!! AT 100mA it is less than 200mV Vf.
 
Since the voltage out of the dynamo is essentially a function of the road speed, it could be quite high. leading to my difficulties in finding low Vf diodes..
 
If I put a pair of zener diodes across the output of the dynamo - before the rectifier, then the rest of the circuit is limited to only that voltage, and the diodes in the bridge recifier are limited to half of that.
 
I am not sure if 20V or 30V is the right target voltage for the rectifier. Higher voltages get more complex, as larger logic level MOSFETs seem to need 5.5 to 4.5V gate voltages rather than 3V, 2.5V or even 1.8V.  Also, low-drop-out v-reg that will take > 30V as input are rare.


I am leaning towards 20V (or 18V to split the diff between LEDs and specs).
A pair of zener diodes across the output of the dynamo - before the rectifier can discard the extra power.


Two 5W 27V zeners will each conduct when the voltage exceeds 27V + Vf of the other diode (1.1V maybe).


If 20V then [http://uk.farnell.com/on-semiconductor/mbrs410lt3g/schottky-rectifier/dp/1702812 10V/1A] seems a useful diode to rectify 0.5A with low losses.


* [http://uk.farnell.com/nxp/pmeg1020ev/diode-schottky-sot-666/dp/8737835 10V 2A, 250mV drop at 0.5A] 10 for a £ :)


== MCU programming ==
== MCU programming ==
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I wonder how the users of SMD packages manage it?
I wonder how the users of SMD packages manage it?
I have copped out and am setting up JTAG :).


== rough design ==
== rough design ==
 
(see actual [http://wiki.london.hackspace.org.uk/w/images/f/f1/Bikelight_09_s.png schema])
* dynamo->AC  
* dynamo->AC  
* AC->2 back-to-back 5% 18V zener diodes->clipped AC. (Clip the input voltage to less than 20V (allowing for error and forward diode voltage) which should be a safe range of rest of components.)
* AC->2 back-to-back 5% 18V zener diodes->clipped AC. (Clip the input voltage to less than 20V (allowing for error and forward diode voltage) which should be a safe range of rest of components.)
Daveb
153

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