Getting feedback on a schematic

[Katzenjammer]

I have a schematic for a bike lighting system that I'd like to get feedback on and help with. As I think I mentioned when I signed up here, I've no expertise with hardware at all (I can rewire a lamp), so my design essentially reflects only the logic, not the electric changes or the glue needed to make it all work.

How should I go about getting feedback? Is this the right forum?

 

[eclectic]

Go ahead.

This is the right forum.
Post your circuit and your program and wait for the replies.

e.

 

[Katzenjammer]

Well, the bleeding file is too big to load here, so it can be found at http://home.att.net/~katzenjammer/bike/Lighting0_150ppi.gif

The schematic is a bit of a kludge, since right now I'm reckoning to build 2 cards identical except for the programming, whereas the schematic pretends that it's all on one card. So you have to imagine the front and rear functions being separated. My thought is that putting everything onto one card would mean many long wires running to the actual lights being managed. Whereas with the functionality separated, the cards can be co-located in the light housings and the only thing I need run is the signals from the handlebar switches, which I think I ought to be able to do with some RJ-11 wire (please correct me if I'm wrong)


The program (still being written - the hw is the hard part for me) isn't at all clever. I simply poll the switches endlessly in one giant loop.

The mode switch decides whether the lights are in daytime (high brightness, flashing head and tail) or nighttime mode (moderate brightness, steady head and tail). Or off, of course.

The default state for the turnsignal clusters is warning. When turning, the two amber clusters on the relevant side flash in unison at a "turn-signal-looking" rate. When not turning, the two outside clusters flash twice in an urgent-looking way, followed by the two inside clusters, in an endless loop bipbip bepbep bipbip bepbep....

At no time do I go into twiddle mode except when debouncing the switches. Otherwise, I keep state information in counters and state vars so that I can service all the lamps via polling rather than playing with interrupts.


As you critique the hardware, I'd appreciate it if you'd help me learn how to think about hw design. Right now I don't at all know how to think about it, except as though it were software which isn't I'm sure very useful. I know about things like voltage drop and Ohm's law, but only in a totally abstract sort of way. For example, although I know that every diode or ic causes a certain voltage drop (.6V iirc), I don't know whether or when I need to do anything about it, never mind what I should do or how.

 

[BCJKiwi]

The first thing that springs to mind looking at the circuit is that much of the hardware could be eliminated by programming.

Just have one light assembly fed from one mosfet fed from one PICAXE output. Programming determines which ports to turn on when and in which combinations.

This eliminates the inverting decoder and all the diodes!

Perhaps it would be better to start with the program, design the schematic, build the circuit on the breadboard, finalise the circuit, then design the board(s).

You could still separate the front/back by using two smaller PICAXEs and having basically the same program in each with the switching fed to both.

Have built a bike light system and put it all in one box using an 18X high power board (only 4 MOSFETS though)! Since the outputs are to LED based lighting and at 12V the loads are not that high and the wires not that long - compared to a car say.

I purchased ready made and certified auto LED light clusters - 4 amber for indicators, and one Red Tail/Brake unit. The Tail/Brake unit was switched directly, not via the PICAXE.

 

[Katzenjammer]

Thanks for your feedback.

Agreed that I can eliminate the decoder by consuming two more output pins, so that would be a good tradeoff if I can find the pins.

You might have to explain your "eliminate most of the hardware" and "Just have one light assembly fed from one mosfet fed from one PICAXE output" in more detail, because I can't picture it.

 

[Dippy]

Katz, woudln't an 18X provide enough outputs?

Each output can control a MOSFET via a resistor to make your switch. I think that is what BCJ is suggesting.

Your on/off can be a P-channel like you have already shown. You can also PWM an N-channel on the 'low side' of your light arrays to make them dimmable (noting possible RFI on long wires and annoying strobe effects of new car rear lights which gets on my tits).
Effectively, you would be switching supply and ground. Make sense?

Have a think about that. Please note that it would take a while to do a schematic for you. Whilst i would love to, I simply haven't got the time. Maybe some kind soul with plenty of spare time can do it.

 

[eclectic]

K.
I'll agree with BCJ.
The 18X high power board is quick and easy to wire, and has 4 high power outputs.

See
http://www.rev-ed.co.uk/docs/chi035.pdf

Page 5 lower diagram.
Remove R9 (p2 lower para)
Then attach the Ground of each reversing cluster to 0,1,2 and 3 respectively.
All positives connect with V2+.

Page 8, circuit diagram V3 shows the wiring layout.

It could also be used as a starter to wire your own 18X + 8 FET board.
(Obviously, there won't be a 293 chip in your circuit.

e.

 

[Katzenjammer]

Thanks for the feedback, all.

Dippy, I'm sorry if it seemed as though I was asking someone to create a schematic for me - nothing could have been further from my mind and I feel more than a little appalled that I could somehow have given that impression.

I think my next step is to buy some parts and try not to cook too many of them.

Cheers.

 

[BCJKiwi]

Hi, Time Zones strike again!

It looks like the circuit is not available on the web anymore so I am unable to be more detailed in explaining further what was meant in my previous post but I assume Eclectic's description is sufficient to expand on my suggestion.

Basically you want to connect one light assembly to one output with the mosfet in between.

Thus programming controls each light assembly directly.

 

[manuka]

Yes- this "no show" caught me too. Katzenjammer: As this forum now allows .jpg uploads to ~1MB, just resize/redo your schematic (as a .jpg rather than .gif) using - Additional Options- Manage attachments etc.

I've become mildly opinionated about bike lighting systems due to both a biking lifetime with this field, AND some near misses as a driver with cyclists who are NOT suitably illuminated! ARGH...

Stick with me, but perhaps clarify for starters- What have you in mind for a power supply? How charged? See or be seen? Are you up with super efficient dynamos (LightSpin, Busch + Müller Dymotec etc)? What ranges anticipated? Get you home mode? Terrain? Mission critical rides? "Standby" mode when waiting at lights etc? Local regulations? THEFT protection? Budget? Your bike or another? These points can be very important in a design, as bright ideas may run out of juice & leave you out in the sticks near blindfolded. You may find your darling has been stolen as well, or stopped working due to rain. Of course,IMHO halogens should now not be considered, as super bright, rugged & efficient white LEDs/Luxeons abound. Stan

 

[Peter M]

Went for a gecko and get a docko no show
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