[help me create a racing timer]

I've been wanting to do the exact same thing. I made a simple timer using lasers that shone across the track into sensors and triggered the timers when the car blocked the laser, but it doesn't work very well because its hard to get the lasers to shine right into the sensors.

I am interested in this 'IR opticial barrier' thing, and would like more details if you could.

Thanks.  ;)

[NiMH Battery Pack Charger]

If anyone can help me out with the charger design (circuit), I would appreciate it.  ;)

Sorry about the double post, but I would really like to complete this project and needed to get it back on the first page where people will see it.

[NiMH Battery Pack Charger]

Thanks again for your help.

Yes.

Sorry to keep asking questions about something so simple, but what value do think I should use? 1K maybe? Or is that too low?

I think the charger circuit will miss detecting the full charge. That's why the battery charger ICs have many redundant circuits (temperature and pressure etc.) to detect just before a battery cell explodes. hopefully their designers have thought of everything and you are just copying their ideas.

So maybe I could check and see if the battery is almost fully charged, and if it is more than, say, 90% it will just use a trickle charge, or maybe a timed charge, then a trickle charge. That way I don't have to worry about missing the increase in voltage.

Thanks.  ;D

[NiMH Battery Pack Charger]

Go to www.maxim-ic.com and look at their 48 battery charger ICs.
http://para.maxim-ic.com/cache/en/results/5099.html
You could also see the rechargable battery tutorials at www energizer.com and at other battery manufacturer's websites.

Thanks. I'll take a look at some of those datasheets.

Without a load, a discharged battery will probably measure 1.2V per cell. So some battery chargers load the battery then measure its voltage.
During charging, if the voltage doesn't increase to what is expected then the battery must have a shorted cell.

It may seem like a stupid question, but how would I put a load on a battery? Would I use a resistor? Also, how long would it take before I could be sure there is a short? If the voltage doesn't increase at all, would I be able to tell right away?

It should detect the voltage rise when the battery is fully charged.

So if the battery is 95% charged, I will still be able to detect a sharper than normal increase, indicating a full charge?

Thanks.  ;D

[NiMH Battery Pack Charger]

Do you think you could give me a link to one of those datasheets? Thanks.

Before charging begins, a voltage measurement should be made that the battery isn't already charged.
During charging, a voltage measurement should be made to determine if the battery has a shorted cell.

So if at the beginning of the charge the voltage is already 1.2 volts, it should cancel the charging? Also, how would I detect a shorted cell by measuring the voltage?

One more question. Let's say you have a battery that is partially worn down, to about 80% or so. Would the charger still work right or would it detect a sharp voltage increase to late?

Again, thanks everybody for the help.  ;D I will probably be able to make the first charger soon. It won't be perfect, but it will be a start.

[NiMH Battery Pack Charger]

Well, I'll figure it out when I get it.

Back to the charger's design. I decided I would still rather use peak detecting (lol, I keep changing my mind). Here is my plan for the charger and the program I will write for the microcontroller that monitors the battery:

First, the charger will begin charging at 1c. Second, there will be a loop that keeps checking the increase in voltage over every half a second or so, and when the increase starts to get larger, it will switch to a timed charge, right? Then third, it will use trickle charge to keep the battery fully charged. This is how the three-stage charge routine works right? Will this technique work?

Also, can someone give me an idea of the circuit I will need. I would like it to be as simple as possible. And remember, I am using a microcontroller to control the current and voltage going through the battery.

Thanks everyone.  ;D

[Where to find XTAL stuff?]

Where can I find pins to solder onto a PCB board for XTAL (servo) connectors, and where can I fund plugs and wire for servos? Thanks.  :)

[NiMH Battery Pack Charger]

I looked all over their website but they don't seem to have any info on the battery.

My favorite is www.energizer.com . At the top of the 1st page select Technical Info, then select Ni-MH Rechargable. You will see a link to their excellent tutorial and a datasheet to their AA cells.

Energizer does have a good site.

[NiMH Battery Pack Charger]

Oops, I forgot about this post!

Anyway, I guess I'll use temperature sensing because that seems to be the most reliable way. I still would prefer peak detecting, but if it won't work for what I need then I guess I won't use it.

I am probably going to buy a Mini LST sometime soon, so I want to build a charger before I get it. Here is the battery it uses: http://www.teamlosi.com/Products/Default.aspx?ProdID=LOSB1202. Can someone give me some help on charging batteries like this? Like, where can I find charging info and stuff on this battery?

Thanks everyone!  ;D

[NiMH Battery Pack Charger]

Thanks! That should help me a lot!

If I were to charge a 7.2V pack, what voltage would I supply the circuit with?

My main goal was to use a microcontroller to contol the voltage and current, so how do you think I could modify your circuit to eliminate everything not needed if I use a microcontroller?

[NiMH Battery Pack Charger]

Thank you so much! I read through the part on charging the batteries and its starting to make more sense.

One thing they didn't make completely clear is whether or not you can determine overcharge by the voltage output. I would like to use this method if it will work, so can you give me some help on how I would achieve this? They said you can't use absolute voltage values, so you would have to detect a certain voltage increase, right?

I would like to make this a fast charger, 30 minutes or less if possible. Will the three-stage charging routine work for charging that fast? Keep in mind that most of the batteries I want to charge will be 7.2V and around 1500 - 3000 mah. I would like adjustable voltage and current rates, though. I want the charger to have a wide range of values to choose from, like 6 - 8.4 (maybe even 9.6) volts and 600 - 3000 mah, even though most of the batteries won't be that low or high, probably somewhere in the middle.

Thanks again!

[NiMH Battery Pack Charger]

Thanks for the info. One thing I don't understand, though. What does 1C mean?

As for the 3-stage charging routine, how does it work? Also, where can I get some info on what temperature to stop the charging at, etc.?

Thanks.

[NiMH Battery Pack Charger]

Actually, I don't have a specific pack I want to charge. I want the charger to be compatible with different batteries.

It may sound like a dumb question, but how would you figure out the max. allowed charge current for a battery?

As for the way of cutting off charging, I want to use peak detecting.

Thanks for the help.

[NiMH Battery Pack Charger]

One of my hobbies is driving/modifying electric radio-controlled cars and trucks. One of the biggest problems, though, is that any good NiMH chargers are 50-100 bucks. So I had the idea to design my own charger. I have not started yet, because I need some help.

First of all, what is the concept of charging NiMH batteries? Say you have a battery pack that is 7.2 volts at 1100 mah. What voltage and current would you charge the battery pack at?

Also, how would I design the charger? Do you simply put x number of volts through the battery? How does the charger know when its done? Is it when the battery can put out the voltage its rated at?

I would like to make the charger to have adjustable settings for different batteries, too.

Any schematics would be helpful.

Thanks in advance for the help.

BTW, I am planning on using a microcontroller to control the voltages and stuff.

[Flashing lights..]

Dudes can u help me in designing flashing or dancing lights or whtever u say tht..

Can you give us some more info? How many LEDs do you want to flash?

The circuits so far i have seen is using and decade counter or some counter chips,, i want to make it purely analog..

What do you mean, you want to use analog? Like no microchips?

Here is a link to a fairly simple circuit using a 555 timer and a 4017 counter chip: http://www.charlton.vic.edu.au/mark/electronics/555_projects/k-rider.html

I'm guessing thats not what you want though, because it also uses a 4017 counter.

[Need some help with a design idea]

That project sounds kind of difficult, especially if you have a limited knowledge of electronics. I don't know much about RF stuff, so I can't help you here, but anything with radio waves is kind of tricky, in my opinion. Hope you get it figured out, though. If I find anything that will help you, I'll let you know. :-)

[Introduction]

Thanks for the warm welcomes, everyone. The people seem so nice here.  ;D I'm glad to be a part of the forum.

[Introduction]

Hello everyone!

I thought I'd introduce my self here, as I just joined today.  :)

I have a decent amount of experience in electronics, and I have had a strong interest in microcontrollers lately. I enjoy building electronic projects for a hobby, just like many people here.

Hopefully I can give and receive help here.  ;)