Microcontroller controlled by pushbutton for LED flashlight

[Arouse1973]

Hi Jeff
Can I just confirm that the last circuit Kris drew is the one your going with? Also what do you actually want the output to do when the button is pressed for less than 500 ms. You say momentary operation, can you clarify.
Thanks
Adam

 

[TenderTendon]

Hi Jeff
Can I just confirm that the last circuit Kris drew is the one your going with? Also what do you actually want the output to do when the button is pressed for less than 500 ms. You say momentary operation, can you clarify.
Thanks
Adam

Yes, his most recent one. It's version 3 in post #74. If the switch is pressed for less than 500 ms, the output follows the action of the switch and turns off when the switch is released (acting like a momentary switch). The output only latches on if the switch is pressed for longer than 500ms, requiring another switch press to turn off.

 

[Arouse1973]

Ah ok so if someone flips the mechanical slider switch quickly back and forth you want the output to flick on and off also.
Adam

 

[TenderTendon]

Ah ok so if someone flips the mechanical slider switch quickly back and forth you want the output to flick on and off also.
Adam

Exactly, but I'm using a momentary push button switch, not a slider switch.

 

[Arouse1973]

Exactly, but I'm using a momentary push button switch, not a slider switch.

Hi Jeff
Ok thanks Jeff, I have ordered a couple of PICs so I can get a demo working my end.
Adam

 

[Arouse1973]

Hi Jeff
Ok I have checked the circuit and apart from one issue all seems to be ok. The one issue I see maybe a problem is the leakage current of the schottky diode. Just looking at the Vishay part, it's leakage current is about 60 uA at 3 Volts at 25 degC, it gets a lot worse as the temperature increases. So we may have to look at a different diode or larger capacitor, but choosing a diode with a higher reverse breakdown voltage should do the trick.
Adam

 

[TenderTendon]

Hi Jeff
Ok I have checked the circuit and apart from one issue all seems to be ok. The one issue I see maybe a problem is the leakage current of the schottky diode. Just looking at the Vishay part, it's leakage current is about 60 uA at 3 Volts at 25 degC, it gets a lot worse as the temperature increases. So we may have to look at a different diode or larger capacitor, but choosing a diode with a higher reverse breakdown voltage should do the trick.
Adam

Here is the datasheet for the actual schottky I ordered:
http://media.digikey.com/pdf/Data Sheets/Microsemi PDFs/LSM115J.pdf

Could you explain (in a language that an idiot like me can understand) the effect that this reverse leakage will have on the circuit operation?

 

[TenderTendon]

If You can't mill one of these, I'll do a couple myself and send them to you.

I have tried everything I have here, and I can't import those plt files with anything. I don't want to give up yet though. Can you convert to IGES?

 

[Arouse1973]

Here is the datasheet for the actual schottky I ordered:
http://media.digikey.com/pdf/Data Sheets/Microsemi PDFs/LSM115J.pdf

Could you explain (in a language that an idiot like me can understand) the effect that this reverse leakage will have on the circuit operation?

Hi Jeff

When you apply a reverse voltage to a diode, the diode is not a perfect insulator so there will be some current even in blocking mode. This current is called leakage current and is normally so small compared to the forward mode current that it is ignored. When you are designing low power circuits this current can be a significant part of your current budget.

All this needs to be taken into account. Now in the grand scheme of things this is not a huge amount of energy as far as the capacity of the battery. But it is significant with regards to the energy stored in the capacitor. See chart below for leakage current of your diode.

We also need to look at the capacitor value with respect to the dv/dt as I think at your minimum voltage of 2.8 Volts and with the diode drop we could be violating the min supply voltage of 2 Volts if the capacitor voltage is allowed to drop for too long. We might be ok because as the voltage drops the current the PIC will draw will also go down. But it is something we need to look at when we have prototyped some PCBs.

Adam

 

[(*steve*)]

I have tried everything I have here, and I can't import those plt files with anything. I don't want to give up yet though. Can you convert to IGES?

I haven't forgotten you. I'll try to do this for you tonight. If I can't produce the format you need I'll produce everything I can

 

[TenderTendon]

I haven't forgotten you. I'll try to do this for you tonight. If I can't produce the format you need I'll produce everything I can

No worries... Take your time.

 

[(*steve*)]

I can't do IGES, but I can do DXF. I note that there are a number of free tools to convert DXF to IGES.

 

[Arouse1973]

My Gerber software can do it. Jeff I have a file for you but it is too big to post here. Give me an email address and I'll send it to you.

Update, PICs arrived today so will be making up a demo PCB to test the software. I am on holiday next week so I don't know how much time I will have. I'll keep everyone updated as I go.

Adam

 

[TenderTendon]

I can't do IGES, but I can do DXF. I note that there are a number of free tools to convert DXF to IGES.

Thanks, I was able to open that.

 

[TenderTendon]

My Gerber software can do it. Jeff I have a file for you but it is too big to post here. Give me an email address and I'll send it to you.

Update, PICs arrived today so will be making up a demo PCB to test the software. I am on holiday next week so I don't know how much time I will have. I'll keep everyone updated as I go.

Adam

Thanks. PM sent.

 

[TenderTendon]

OK, you think this will work?

 

[Arouse1973]

Woooow well cool. You just did that. I wants one of thems. What did you do that with?
Adam

 

[TenderTendon]

Post #82 explains it. Do you really want one? I can cut another..

 

[Arouse1973]

I meant the machine you used. That looks really good.
Adam

 

[TenderTendon]

A Tormach PCNC1100.