User talk:Daveb
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. Parts ideas: 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.
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. 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.
- 3.0v, 200mV drop out, 50 mA, max 40v supply gets 2.8v MCU supply after a 200mV diode, from a 3.2V supply :). It is a 4 pin SMD device for £1.60.
- 3.0v, 120mV drop out, 50mA, 16V max supply will do above from a 3.12V supply, but restricts me to chains of fewer than four LEDs. £0.46
- 3v, 350mV drop out, 100mA, 30V max supply is a small 3 pin through hole package for £0.46. Supply voltage is now 3.35V :(.
For 1.8V MCU ..
- a 2.5V, 300mV drop out, 100mA, 20V max power supply will allow operation at 2.8V:).
