LED Timer

[edeca]

I would like to make a simple timer with a number of LEDs to show how much time has gone by.

[gogo2520]

Hello  edeca

  That could be done with a 555 time and a 4017 counter and some kind of gate for em plus transistors and resistors, and caps. Or a Pic could be multiplexed on one port to handle the 10 led's but you would need to use transistors to handle the curent for the leds. If I were to try this project I would go  the 555 timer way.
                                                                good luck
                                                                  gogo

[edeca]

Thanks for your ideas!

[MP]

I am not sure why your simulation fails since I rarely use any of the simulation software packages. However, to answer some of your other questions, the LEDs will each go on and then off as the signal is sent to the next LED when using a 4017. Use of large capacitors on the LED side of the 4017 would give you some delay, but would not keep them on like what you want. Another method you could use to achieve this goal is to use a LM3914 as a voltmeter setup and feed the varying steps of voltage to the chip to cause the LEDs to light up in sequence. The LM3914 has the capability to keep the LEDs lit as you progress. This is how audio meters are made, with the exception that they use the LM3915, which has a logarithmic progression instead of the LM3914, which has a linear progression like what you want.

I noticed that you mentioned a PIC programmer. Another method is to use a microcontroller to run a timer and set the ports high or low as needed.

MP

[edeca]

Thanks MP, that's really interesting!  I like this idea and I'm looking at the datasheet.  What would be the easiest way of feeding it a slow voltage increasing from 0v to 5v or 9v?  Can it be done with a simple capacitor charging circuit?  If so, I'll have a look for some information and try to build one.

Ideally I'd like the circuit to work with as little battery power as possible and this seems like a good solution.

Thanks again!

[audioguru]

Ideally I'd like the circuit to work with as little battery power as possible

LEDs need a fairly high amount of current. If they all turn on then the current is 10 times as much as if only the indicating one is on.
Choose a circuit that lights only the indicating LED.
Select very bright LEDs that need a very low operating current.
Select low voltage (red) LEDs.
Choose a circuit that operates from a low voltage instead of wasting 7V from a 9V battery.
Use a Cmos 555 (or a Cmos inverters oscillator)instead of an ordinary 555 that needs a fairly high supply voltage and uses a fairly high current.

Your timing is very slow so the indicating LED could blink to save battery power, like in the LED projects I have posted on this site.

[MP]

Hi edeca,
Sorry for the late reply. Yes, you could use a charge pump circuit to get you the slow signal that you want. There are probably a lot of different ways to do this. One way to do it is to use CMOS switches. Also, some digital gates with capacitors to smooth out the signal would work. A slow sine wave oscillator could also be used for the front end of a circuit like this. You would need to look at the possibilities and choose what suits you best.

MP