Hi there, names Chris, I'm an aircraft electrician currently working F-16's. I took on a project build and I seem to have jumped in way over my head. My commander is retiring and I've been asked to build a beer cooler out of an old toolbox. So I decided to get all fancy like with it. I want to put two 1W White LED's on top that "throb" together like navigation lights on a plane do when you turn the box "on". When you open the lid I have two LED backlighting panels that will shine down onto the inside of the box. All of this was to be powered by a 3.7v 2500mah LiPo battery.

I thought I had it all figured out and went to proto it when I realized, oh no, 555 timers don't work with voltages under 5v. So I started to scour google looking for something that would be similar and I couldn't really find anything. I came across a few threads by Bill Marsden on 555 timers and some things about 7555 timers and their capability to be powered by 3v power supplies. So I am pleading with All About Circuits forum community for help with my project. I'll post my component list and a kind of mock up I have of how I wanted things to go in subsequent posts. And if anyone is interested, I'll post pictures and a video of the builds progression once I have it all figured out.

 

• 3.7v 2500mah LiPo Battery
• USB/DC/Solar LiPo Charger
• Huge 6V 5.6W Solar panel
• 2x 1W Cool White LED
• 2x White LED Backlight Module
• Waterproof Metal On/Off switch
• Microswitch w/ roller lever
• Large tin w/ clear top
• Various passive components from some Jameco electrical kits/Radioshack

 

Kind of, I tried. I know its retarded, but hopefully anyone who views this gets the idea.

 

Upon further research I have discovered that 7555 IC's aren't the only ones that allow for a lower supply voltage; ILC555 and TLC555 allow for 2v supply voltage. I will order some of these and hope that I can use them in one of the many "throbbing" LED circuits I have found through Google. I have also ordered more transistors and capacitors and 25 7555 IC's just in case. Unfortunately my local Radioshack doesn't have a very robust selection of DIY parts so I have to order everything online. I understand that 555 IC's have a voltage drop. Does anyone know if using a CMOS 555 with a 3.7v LiPo battery will prevent my LEDs from powering on? Also what does "maximum power dissipation" mean?

 

What is your time frame?
Do you already have listed materials in hand?
Are the back lit panels bright enough?
With batt V almost LED Vf, might need PWM throbbing

What is your approx location?.

 

What is your time frame?
Do you already have listed materials in hand?
Are the back lit panels bright enough?
With batt V almost LED Vf, might need PWM throbbing

What is your approx location?.

Yes I have the parts listed in hand, the new transistors, capacitors, and 7555/TLC555 timers will probably be here by the end of the week. I also have breadboards, perma/proto boards, a bunch of jumper wires, some hookup wire, a Dremel 4000 and a Hakko 888 soldering iron. I really thought I was ready to proto and then build. Time frame, I'd say a week or two, I was really hoping to get it done this week but with the 555 timer delay, I'm probably going to push it to the end of next week. I'm in Fort Worth, TX.

 

My thinking is to use 2 C555 , 1 200Hz fast triangle gen. 1 for slow, about 5 sec. period for slow clock. Outputs fed into a LM393 comparator. Re look up Bills Index, Ch 5 using 555 & LM339. Second C555 takesplace of voltage divider. LED driver needs to be modified due to low output capability of lo V power supply operation. I'll be back later today.

 

I'm at work now, I've been working on this project burning the midnight oil. But I looked at his lessons for 555 timers and LED flashers and such. The only issue I have is I have to use the LiPoly battery now. I've already sunk so much money into this project already. I don't think I can use the ICM7555 timer though, its output is only 20ma which would be fine for some 5mm LEDs but the ones I'm using are at least 350ma. Do you think with a common "throbbing" circuit and a TLC555 I'd be okay? The TLC555 supply voltage can go as low as 2V and outputs 1000ma. But I also am wondering what kind of voltage drop the TLC555 has. And if its a significant drop, do I need to also put in a boost driver? Will the boost driver prevent the LEDs from throbbing?

 

I'll check but C 555 output is more like 100 mA low out & 10 mA high with a Vcc of 12 V, @ 3V drive will be less. Throbbing will not be effected. @ 350 mA each, that is 700mA pulsed.

 

Okay, so I need a way to boost 100mA to 700mA after the output of the TLC555? The 1W LEDs are 350mA a piece, and the backlighting modules are 20mA a piece, I think. Looking at their datasheets on Adafruit that's the conclusion I came up with. I still need to figure out resistor values as well. The two backlights tap straight off the battery charger, and the two throbbing LEDs come after the timing circuit.

 

Finally put it on paper. Throbbing just like Bill's PWM ckt with added slow trianglr wave train. V divider R2- R3 raise slow sig a bit so that the LED's never go completley out, on times 3% to 100%. I do not know the Vf of the 1W LEDs, were tested with 3 V 2W LED. FZT849 is med power SM NPN, 7A, 80V, β about 100. Others will also work. Under charge, 4.2V,? LED current might climb to 600 mA. Other option , use boost constant current converter that accepts modulation.
All Rs 1/4 W, Any parts that you still need without a minimum order, I can supply.

 

Would an LM2903 work? When you say C555 is that in reference to TLC555? I'm not at home so I'll have to check to see if I have the LM393 and that other one. Thank you so much for providing this. And being patient with me.

 

LM2903 same for our purposes, same for TLC555 = C555.

 

Finally put it on paper. Throbbing just like Bill's PWM ckt with added slow trianglr wave train. V divider R2- R3 raise slow sig a bit so that the LED's never go completley out, on times 3% to 100%. I do not know the Vf of the 1W LEDs, were tested with 3 V 2W LED. FZT849 is med power SM NPN, 7A, 80V, β about 100. Others will also work. Under charge, 4.2V,? LED current might climb to 600 mA. Other option , use boost constant current converter that accepts modulation.
All Rs 1/4 W, Any parts that you still need without a minimum order, I can supply.

I noticed that the FTZ849 is a SMT component, would a ZTX849 work? Its through hole and I plan on doing this on one of those perma-proto boards. Although I guess I could just cut the legs off of a different transistor and solder them to the FTZ849 to make it through hole (right?). I found all of these on mouser and none of them are minimum order so I'm pretty sure I can get them myself.

Really, thank you for your help. The schematic you came up with is way more advanced than anything I've seen elsewhere and so much better than anything I could have come up with on my own (I'm sure you saw my mock up...). I'm going to order these parts/source them at Radioshack and then see if I can breadboard this up over the weekend. Thank you so much for your time, I'll post up pictures of the build progress as soon as I can

 

ZTX849 looks good. You could use a pot, around 1M, for R1 to select a pleasing throbbing rate. Fast clock is non critical, 100 Hz to 1 kHZ.

 

Is C1 a 5uf capacitor?

 

Yes, any value that gives desired throb rate, about 1.7 R1C1.

 

Pretty much perfect Its exactly what I needed and I got it all proto'd up!



I know its probably a mess by most peoples standards, but this was my first time breadboarding, and I'm pretty happy that I got it to work. Videos in subsequent posts

Or...

Links to videos:
Two Throbbing 1W White LEDs
Two Throbbing 1W White LEDs, one with "green" cover

They're so bright.

 

With V supply at 3.7, LEDs are operating around 350 mA, but if charger is connected while operating, battery might go to 4.2 V which means 600mA LED current. If desired a simple verry low drop out regulator could be used. The one I lashed up works on a breadboard but not tried with throbbing ckt as it was already broken down. It uses same LM 393 with power moved over to battery input. As battery V falls, V out stays at set point untill bat. = set, the output falls in lock step with batt there after untill about 3 V where output disconnects. There is some trash on the output.

 

With V supply at 3.7, LEDs are operating around 350 mA, but if charger is connected while operating, battery might go to 4.2 V which means 600mA LED current. If desired a simple verry low drop out regulator could be used. The one I lashed up works on a breadboard but not tried with throbbing ckt as it was already broken down. It uses same LM 393 with power moved over to battery input. As battery V falls, V out stays at set point untill bat. = set, the output falls in lock step with batt there after untill about 3 V where output disconnects. There is some trash on the output.

Unfortunately, by the time I saw this, the original circuit was already built for the box and I didn't have the components I'll just let the receiver know that he shouldn't use the box while its plugged in if he doesn't want it to catch on fire...