Please review my noob circuit!?

Thread Starter

ponderosa_74

Joined May 5, 2013
10
Hi,

I'm really new to electronics, soldering, etc. - started about 3 wks ago. I'm building an airport for my 2 sons ages (almost) 3 and (almost) 5. I want to have 4 LED's to illuminate gate signs, 2 hobby motors that control rotating radars, and another set of alternating/blinking LED's for the top of the control tower. Ideally, I'd like them to be on one circuit running off one rechargeable battery, like a LiPo used for R/C aircraft, so we don't have to keep buying batteries.

Please see the attached schematic, this is what I came up with:
1. 4 x 2.2V, 20mA LEDs connected in parallel
2. 2 x 3.0V, 30RPM hobby motors connected in parallel, I could not figure out the current draw from the motors, I tried with a multimeter but the numbers were fluctuating all over the place.
3. 1 x 555 blinky from MAKE magazine (http://blog.makezine.com/projects/555-timer-blinky/), which is running off 4.5V (3xAAA), but not sure of voltage drop of this subcircuit or the current draw,

--1, 2, & 3 above are in parallel with each other (please see schematic)

So my questions are:
Will this work with what I have there?
Is there too much resistance to prevent current from flowing to the 4LED's?
Do i need more or less voltage from my battery?
Could I use a LiPo battery for this, if so, how do I decide which one is best (they're described in mAh, which I don't really know what to do with?

I know I could probably find answers somewhere, but I dont have alot of time for proper research so thanks for tolerating my questions, and many thanks in advance for any advice/help!

-ponderosa_74
 

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kubeek

Joined Sep 20, 2005
5,599
For the LEDs I get 360 ohms, wonder how you got to 150. If you can´t get 360, you will probably be able to get 390ohms.

For the motors, use a 6.2V zener diode instead of the resistor, with the "arrow" pointing up. It should have double the power rating of the motor.

If you are using LM555 for the blinky, you can safely use it for up to 15V supply, you only need to change the resistors in series with the two leds to 390ohms or so. Also I suggest adding another 0.1uF cap across the suply pins of the 555.
 

Thread Starter

ponderosa_74

Joined May 5, 2013
10
For the LEDs I get 360 ohms, wonder how you got to 150. If you can´t get 360, you will probably be able to get 390ohms.

For the motors, use a 6.2V zener diode instead of the resistor, with the "arrow" pointing up. It should have double the power rating of the motor.

If you are using LM555 for the blinky, you can safely use it for up to 15V supply, you only need to change the resistors in series with the two leds to 390ohms or so. Also I suggest adding another 0.1uF cap across the suply pins of the 555.
thanks for the reply, i was editing that photo I think when you replied!
the zener diode is just preventing too much voltage getting to my motors? with the arrow pointing up, when i put it into my circuit simulator, it shows current flowing backwards??
what is the capacitor for the 555 your are suggesting for?

MANY thanks!
 
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kubeek

Joined Sep 20, 2005
5,599
Yes, ratshack seems to have them http://www.radioshack.com/product/index.jsp?productId=12614293 (but I´ve never seen such horribly unusable web site). Seraching for zener 6 will get you a few other hits, but this one seems the most reasonable.

The capacitor is to smooth out the powersupply of the 555, it is a general practice to put one close to each IC´s power supply pins.
 

tubeguy

Joined Nov 3, 2012
1,157
If you want to maximize battery efficiency, use a lower voltage (4.8 v supply. for example)
and recalculate resistors.

mAh refers to milli-amp hours.
2000 maH = 1 hour at 2000ma or 10 hours at 200 ma.
 

Thread Starter

ponderosa_74

Joined May 5, 2013
10
Yes, ratshack seems to have them http://www.radioshack.com/product/index.jsp?productId=12614293 (but I´ve never seen such horribly unusable web site). Seraching for zener 6 will get you a few other hits, but this one seems the most reasonable.

The capacitor is to smooth out the powersupply of the 555, it is a general practice to put one close to each IC´s power supply pins.
thanks! i was looking for it there, too. yes, their site leaves much to be desired. the in-store experience is worse!
 

Thread Starter

ponderosa_74

Joined May 5, 2013
10
If you want to maximize battery efficiency, use a lower voltage (4.8 v supply. for example)
and recalculate resistors.
Would that be enough voltage if I wanted to run everything at the same time??


mAh refers to milli-amp hours.
2000 maH = 1 hour at 2000ma or 10 hours at 200 ma.
thanks, so it's just a matter of how much use the battery to get at full current draw, correct?

thank you!
 

Thread Starter

ponderosa_74

Joined May 5, 2013
10
Wouldn't the motors run only when the LEDs are lit?
?? - the set of 4 LED's are in parallel with each other and then are in parallel with the motors -- are you thinking they're in series with the motors? look at the schematic in the original post, which is probably better than my text.

thanks!
 

tubeguy

Joined Nov 3, 2012
1,157
Would that be enough voltage if I wanted to run everything at the same time??

thanks, so it's just a matter of how much use the battery to get at full current draw, correct?

thank you!
1. Yes because you need only enough voltage to run the highest voltage component. The determining factor in this case is the 4.5 volts needed for the 555 blinker.

2. Yes (I think) :)
To pick a battery capacity (mah) calculate the total current draw and multiply it by a reasonable run time.

If the LED's are rated at 20ma maximum current you really should run them at less - maybe 15 or even 10 ma. You should still get acceptable brightness.
 
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LDC3

Joined Apr 27, 2013
920
You can drop current requirements by using the CMOS equivalent of the 555 timer; I think the number is 7555. It using the same voltage range, but much less current.
 

LDC3

Joined Apr 27, 2013
920
If you mean 5mA is "much less". This is quite small compared to the OP's loads of LEDs and motors.
The 7555 timer typically has a static supply current of 60 µA using Vcc of 15 V, and lower currents for lower voltages. This is 100 times less current than a 555 timer at 5 mA. Since ponderosa_74 wants to run the circuit off batteries, saving all the current for the LEDs is important for longer operating times between recharging the batteries.
 

Thread Starter

ponderosa_74

Joined May 5, 2013
10

Thread Starter

ponderosa_74

Joined May 5, 2013
10
You can drop current requirements by using the CMOS equivalent of the 555 timer; I think the number is 7555. It using the same voltage range, but much less current.
i've already ordered a couple 555's, but i assume you're implying the 7555 provides the same functionality?
 

Thread Starter

ponderosa_74

Joined May 5, 2013
10
1. Yes because you need only enough voltage to run the highest voltage component. The determining factor in this case is the 4.5 volts needed for the 555 blinker.

2. Yes (I think) :)
To pick a battery capacity (mah) calculate the total current draw and multiply it by a reasonable run time.

If the LED's are rated at 20ma maximum current you really should run them at less - maybe 15 or even 10 ma. You should still get acceptable brightness.
Great, thanks for all the help!
 

Thread Starter

ponderosa_74

Joined May 5, 2013
10
I'm actually running into some issues with my schematic - I incorporated a lower voltage battery, added in zener diodes and just cleaned everything up, but I'm getting some odd current and voltage fluctuations that I don't understand. I will post within the week.

Thanks for all the help
 
If you want to maximize battery efficiency, use a lower voltage (4.8 v supply. for example)
and recalculate resistors.
 
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