User talk:Daveb

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Dave Brown - hacker in spirit.

Project Ideas

Project Status Notes
Reconfigurable sailing proa plan Rob Denny at http://www.harryproa.com has some interesting things to say about Proas and how they could be the basis for a cheap, high performance, spacious sailing cruising boat. Perhaps the ideal cruising boat :). I want to explore the sailing characteristics in a model.
LED lights and lenses for my bike plan http://pilom.com/BicycleElectronics/DynamoCircuits.htm explains the matching of LEDs to bike generators. I plan to have several strings of LEDs with different beam angles and aiming points - and the appropriate string of LEDs turned on for the curent bike speed.
LED lights in walking stick idea Want to combine a torch and walking stick for my father. Should be reliable over several years, have little impact on the walking stick, and provide light when needed with no manual switch.

Project Status

Bike Headlight

Have ordered LEDs, reflectors and lenses. Have an attiny85 from the space components. Still need a dynamo, some diodes, mosfets, npns, a circuit and some firmware - oh and maybe a heatsink for the LEDs:). The project is moving along.

Have received the LEDs (white Lambertian (but not the reflectors etc).

Still thinking about what the maximum voltage for the LED strings will be ..

At 0.7A and 25deg junction temp, voltage per LED varies between 3.03(min), 3.7(typ), 4.47(max). And 3.9V(typ) at 1A current.

Some uncertaintity - current might just get to 0.5 A but I am sure the junction will be hotter than 25C, and see but no indication of change in V drop with temp in the datasheet :(.


Assume 4.0V per LED - gives 16V for 4 LEDs, and 24V for 6 LEDs.

Switches for LED current

  • This 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 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 SMD MOSFET is 2A mosfet, with Rds of 0.07 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. There is quite a lot more choice at max Vds of 20V.

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

I need to establish the maximmum operating voltage!

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.

For 2.7V MCUs these are the possible best regulators.

For 1.8V MCU ..

Diode to isolate MCU

This diode should allow the MCU to be reprogrammed in circuit, without blowing up the vreg or anything else with badly applied voltages.

It is a dual common cathode part.