is the race at daytime? if so, the led's will not nearly blind anyone, in fact, they will only just be visible

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24-hour-straight race, starts at either noon or 1 PM on the saturday and finishes at either noon or 1 PM on the sunday, the LEDs will only be running at night (between say 6 PM and 6 AM) but i am hoping (assuming i have enough battery power) to have the rest of the PIC running during the day, so that it can lap count based on distance (track is approx 2.4 Km from memory)

I have been looking for a simple programmer for the 16F88, but i cant find one I assume they dont exist.

can anyone recommend a programmer (it only hast to do this 1 model of chip and I need it to be cheap)

this is the one I was looking at http://www.best-microcontroller-proj...r-circuit.html but i fear it may be a little expensive and needs a high voltage (15V)...


I also just realised that MikroBasic programs via the USB port, but Im not sue if i will need drivers and a special programmer to use it, however it can build the code, so I assume i could use another piece of software to programm the chip, whilst writing and compiling the code in Mikrobasic. is this correct?

 

if you use a pic, it has outputs strong enough to drive standard leds, without transistors. if you run your pic at 5v, you can run two red / yellow leds off each output, regardless if you do doubled sided or not, it doesn't "cost" anything extra power wise to run two leds, and you get double the brightness from it.

a good pic programmer will be expensive. I think this is mainly why atmel chips have been becoming more popular, they are cheaper to program. perhaps your teacher or school has a programmer you can use?

the magnet doesn't have to be super powerful. just make sure you get a more sensitive hall effect sensor. they come in different gauss / tor ratings, so weaker magnet = more sensitive sensor. also remember the inverse square law, double the distance between sensor and magnet, 1/4 the field strength. so the closer you can align the magnet to pass the sensor (without nocking into it), the more powerful the field strength will be.

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well, i cant use red, red can only be used at the back of the vehicle, but yellow should be ok. running at 5V will mean extra batteries, but hey, if its not too heavy and the batteries last the 24 hours with 12 hours LED time then im happy to use them - thats 4 batteries to get the full 5 volts, but i think 3 will have to be the maximum.

As for the programmer, im going to try and find a cheap-ish one, i just need a decent schematic. The price of the programmer isnt critical, cause i can use it for other projects so th price isnt too much of an issue.

The teacher may have one, but i doubt the school will, as they dont teach digital electronics since no one signs up for it (its a Hess R subject, which i bad if you want to go to Uni, so no one takes it).

I have ordered 3 16F88 so i will be definately using a PIC.

I guess i'll have to test the magnets and if they arent strong enough i can mount them closer. Good thing you reminded me about the inverse square law, i'll need that for end of year exams

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if you're using throwaway batteries, 4 of them will get you about 6v, which is OK for the pic. it also will give you more runtime as the voltage sags.

three batteries won't give you enough to run two leds in series (yellow has a Vf of 2v), and just running one yellow you're wasting 1.6v on a resistor. you could switch to green, but then you're cutting it close on the voltage, assuming a Vf of 3.3 for green/blue/white leds.

there's lots of threads on this board regarding cheap pic programmers, just browse around the micro controller forum a little.

__________________
If you don't have a planet, what good are gold bars?

want to contact me directly? gmail gordonthree
check out my project website: http://projects.dimension-x.net
Favorite numbers:
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Microchip is actually very good at handing out free samples of their chips. You'll need a non-yahoo/hotmail/etc. email account, though:

http://sample.microchip.com/Default....stCookies=true

Also, I've found that reed switches work well (perhaps even better), and they in general cost less than an Hall effect sensors.

As for LED brightness, I would get the brightest you can find. Then you can run them at lower currents to save on battery power.

Figure out a way to mount the batteries as close to the wheel center as possible. I rode 40 mi. with a bicycle pov on my back wheel, and I definitely had to work harder to pedal it. I also didn't distribute the batteries evenly around the wheel, so there was an imbalance which was very noticeable at higher speeds.

Finally, consider using AAA's instead of AA's. They are 1/2 the weight but still have 1200 mAH which probably will be enough to power you through the entire race - it all depends on your LEDs.

 

well, i hadnt decided on the batteries, i was leaning toward AAA rechargeable Ni-MH, but I dont know that rechargeables have enough mAH in them, so throw-aways are more likely. another option I may have is to use 1 of those 12V batteries and pull the shell off to get the cells inside.

as for the LED's i dont think i will use the brightest, cause they are expensive, then again I could order those ones off ebay... they didnt seem too bad.

what kind of viewing angle do i need, is it the higher the better or the lower the better? im guessing higher.

I'll have to have more of a look thisafter noon cause i have school now, I'll also make sure I ask my teacher about a programmer, although i doubt he or the school will have one.

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"The glass is neither half-empty, nor half full, it's just twice as big as it needs to be" - Unknown

 

You might ask around to see of there is a robotics club in your area - they could be very helpful for a project like this.

 

Instead of a Hall Effect sensor, it might be easier on your schedule to synchronize to the wheel with something simple like a leaf switch. It should offer a very small drag.

Are these solid wheels or spoked?

If you choose AVR you can build a programmer for almost free. And you can use a trial version of BASIC. It only supports programming half of the memory (for free) which hopefully is enough.

 

I dont think there is any robotics clubs nearby, but i dont know if they would be much help.

Will a Hall Effect Sensor require extra electronics to interface it with a PIC?
A reede switch may be the way to go, but from what I hear they are too slow for a spoke project as wheels can turn too quickly.

The wheels are spoked and on 1 side (the external side) we put hubcaps made of corflute, which is like 3-ply cardboard except its made of plastic, and is easy enough to put holes in to poke LED's through.

Yeah, i know about the AVR programmer, but i could find a version of Basic I could use for it and i asked in the Microcontroller forum, but no one seemed to know there. Although it hasnt quite been 24 hours, but oh well...

Oh, and I may be able to build a programmer for my final electronics project, which we are starting next week (whilst finishing our current one)

Thought about rain proofing, will probably put the main circuit in a zip-lock bag and some hotglue waterproofing on LED legs.

Still need to find some LED's, the problem with ebay is the shipping cost of $10

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"The glass is neither half-empty, nor half full, it's just twice as big as it needs to be" - Unknown

 

Ok, I have compiled a small list of links to LEDs that I think would be suitable, what do you guys think?

These are 3 packs:
http://www.dse.com.au/cgi-bin/dse.st...uct/View/Z3891
http://www.dse.com.au/cgi-bin/dse.st...uct/View/Z3892

Singles:
http://www.dse.com.au/cgi-bin/dse.st...uct/View/Z4034
http://www.dse.com.au/cgi-bin/dse.st...uct/View/Z4033
http://www.dse.com.au/cgi-bin/dse.st...uct/View/Z4035


Oh, and at the prices im finding, we will probably stick to an 8 LED display.

You are more likely to know what will and wont work, so after looking at thiose, do you think they will be any good?

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"The glass is neither half-empty, nor half full, it's just twice as big as it needs to be" - Unknown

 

maybe Futurlec, an Australian company, delivers to AU faster than they deliver to the US ... lots of cheap led there. www.futurlec.com

Don't worry about rain proofing. at the voltages you're using, you'll need salt water to conduct any voltage, and likely it'll just cause some corrosion. once you get it assembled and tested, paint the circuit board solder joints with some sort of anti-rust paint and you're done.

a hall switch or a reed switch both require one line from the pic. the hall switch needs to be pulled up/down, powered and grounded. a reed switch needs to be pulled up/down and grounded. so one less connection for the reed switch vs the hall. If you use one of the pins with an internal pull-up on your pic, then you're down to only needed two connections for a reed switch, signal and ground.

problem with a reed switch is response time and longevity. Most switches are only rated for a few thousand contact closures, and in the course of their normal life, this would be years and years. but spinning on a hub at 60+ RPM, you quickly accumulate thousands of contact closures. if this is a one time use project, it won't make much difference, if you want it to last, go solid state. Another thing about reed switches - they're spindly pieces of metal inside a glass tube, sounds kinda fragile to me, compared to the hall sensor which is just some silicon sealed in a block of epoxy.

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ok, im happy to use a Hall effect sensor, its less fragile, will last longer and seems easy enough to use, i was worried i would need an amplifier of some type, but now i dont think i will.

well, this is more then 1 time use, once a year for 24 hours for as many years as it lasts/is still wanted/still fits in the rules.

now, i just want to double check with you on these LED ratings
i dont think this one will be any good, the Forward Voltage is too high, correct?

Blue Super bright from futurlec
Symbol----Parameter----------Conditions ----------Typ----Max ---Units
Vf--------Forward Voltage----Vcc=Min,Ii=-12mA-------3.5----4.0 -----V

But the Orange or Yellow should be OK?
Symbol----Parameter----------Conditions ----------Typ----Max ---Units
Vf--------Forward Voltage----Vcc=Min,Ii=-12mA--------2.1----2.5-----V


Thankyou so much for all your help, once i have confirmed the colour with my teammates ill be ready to start building.

__________________
"The glass is neither half-empty, nor half full, it's just twice as big as it needs to be" - Unknown

 

A digital output Hall-effect sensor will have a built-in-amplifier. There are linear output versions, but you'll want to use a digital one.

This is the interesting part of the engineering... you have to decide:

- what voltage to run your PIC and any other support chips at
- what voltage to supply to your LEDs
- how to provide that voltage (some number of 1.5 volt alkalines or some number of 1.2 volt NiMH cells or maybe a 3.7 volt Li-ion battery)

For instance, if your PIC can run at 3 volts, you can get away with two 1.5 volt alkaline batteries and you can drive red, yellow or orange LEDs (but not blue or white). Also check the voltage requirement for the Hall-effect sensor to ensure that it can run at 3 volts - some require 5.

 

those ratings are excessive for the leds ... red/yellow is going to be 1.8 to 2.0 volts, I'd consider 2.2v to be "high". for blue/green many of them are rated 3.5v but I find 3.0 to 3.3v to work excellent. 4.0v is definitely excessive

pc88 brings up a good point, and that is to be careful in your selection of hall effect sensors. I've found there to be at least three types:

linear: outputs an analog voltage or current in relation to field strength

latching aka unipolar: works like a toggle switch, North field polarity turns it on, South field polarity turns it off

non-latching aka omnipolar: works like a momentary switch, on when field is present, off the rest of the time.

you want the non-latching variety, since you just want a quick HI-lo each time the magnet passes the sensor.

__________________
If you don't have a planet, what good are gold bars?

want to contact me directly? gmail gordonthree
check out my project website: http://projects.dimension-x.net
Favorite numbers:
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0