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Switching a Powerboost On/Off


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#1 RestoLynx OFFLINE  

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Posted Thu Mar 9, 2017 3:56 AM

Looking for some advice:

 

Was thinking of using an Adafruit powerboost for my Lynx, bypassing the 9v circuitry, but the problem is that the original on/off buttons don't work then, correct?

 

The Powerboost will switch on if the EN pin is brought to battery voltage and off if grounded, is that correct? If so could you not re-purpose the on and off button to connect the powerboost to Batt+ and GND, or are they hardwired in the flex circuit preventing that?

 

(Of course another hacky way to do it would be to boost the 5v from the powerboost to 9v using a DC-DC converter like this, I'd lose a load of efficiency and I'd have to switch off the powerboost separately... actually.. that is a terrible idea...)

 

Thanks

 

 

 



#2 af0l OFFLINE  

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Posted Thu Mar 9, 2017 4:51 AM

I have been struggling with the same problem. I ended up poaching a design from the net somewhere to do just what we want:

 

IMG_0090.PNG

 

It's theoretical ATM (ok, working at the protoboard), but I'm sitting on my fathers neck (he does circuits for a living), until he corrects this and makes it into something I can put into my lynxes. As for the buttons - I have ruined my flex unplugging and replugging it so many times, so I came up with this:

 

IMG_0095.jpg

 

Now I can tap into any signal I need from the flex, and most importantly, take it apart without ruining it. It includes replacing the connector on the board, but it does not take a soldering ninja to do it. On the other hand, you might be able to find the signals on board and skip this part completely...

 

I'll report back when the circuit is done.

 

 



#3 Level42 OFFLINE  

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Posted Thu Mar 9, 2017 5:28 AM

I solved it using a LTC2950:

 

 

http://atariage.com/...lynx/?p=3573214

 

Here's the schematic I made:

 

http://www.digikey.c...r-SBA3UE82001G/

 

 

(Notice that I only used the Power On button on my "perfect" Lynx since it was very hard to cut all traces around the Power off button. Both buttons obviously need to be isolated from the original traces on the Lynx !

 

Also: I didn't use external LEDs for the Powerboost in the end so ignore that on the schematic.


Edited by Level42, Thu Mar 9, 2017 5:29 AM.


#4 af0l OFFLINE  

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Posted Thu Mar 9, 2017 11:29 AM

I solved it using a LTC2950


... if you can solder like a champ :)

#5 RestoLynx OFFLINE  

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Posted Mon Mar 13, 2017 6:05 AM

How about this, it takes usb at 5v, charges an 18650 (or two if you run in parallel) and outputs 9v

 

http://www.ebay.co.u...2-/252555626825



#6 af0l OFFLINE  

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Posted Mon Mar 13, 2017 12:11 PM

That would keep you in 9v domain, I'm not sure, but I did not want that, due ti the risks it poses...

#7 Level42 OFFLINE  

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Posted Mon Mar 13, 2017 2:45 PM

... if you can solder like a champ :)

 

Really not so hard with the PCB....just need to be VERY careful with the glue....



#8 af0l OFFLINE  

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Posted Mon Mar 13, 2017 2:51 PM

 
Really not so hard with the PCB....just need to be VERY careful with the glue....


I have two legless nano chips that say otherwise :)

#9 RestoLynx OFFLINE  

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Posted Wed May 10, 2017 3:53 AM

Ok, that 9v module didn't work, I'm guessing that it isn't supplying enough current as I get the flashing battery light.

 

I got a Powerboost 1000c but I'm having a lot of trouble; it only seems to be capable of starting the lynx about 10-20% of the time, it's infuriating, the rest of the time the screen (McWill) just shows garbage, once it starts it stays running happily. Whether the batteries are connected or it's running off usb it's the same behaviour.

 

I made the power wires thicker and it worked for a while(on the bench), but then when I popped it into the lynx and tidied up the wires it went back to its old ways. 

 

I'd appreciate any thoughts you might have, ask me questions, I feel like I'm missing something here.



#10 RestoLynx OFFLINE  

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Posted Wed May 10, 2017 12:47 PM

How about I bypass D9, the reverse protection diode? that should get me another 0.7V if I'm at the lower limit of voltage? I'm not going to be using the AC adaptor, or AA batteries and I can remove the bypass if I decide to go back. Is this a terrible idea or a great solution?!!



#11 af0l OFFLINE  

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Posted Wed May 10, 2017 1:01 PM

How strong is your psu?

#12 RestoLynx OFFLINE  

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Posted Wed May 10, 2017 3:10 PM

How strong is your psu?

It's 2 Amps, which should be enough. The behaviour is the same whether it is running from usb or the charged LiIon batteries. :(



#13 af0l OFFLINE  

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Posted Thu May 11, 2017 2:43 AM

Hmm, 2 Amps should be ok. It also happens to me sometimes, although much, much less frequently...



#14 af0l OFFLINE  

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Posted Thu May 11, 2017 2:44 AM

OH!

 

Now I see it! I don't have EN connected, I just ground it when I want to disable the Powerboost. I don't think you should be connecting it to battery voltage  :?

 

That's:

 

EN --- GND  = OFF

EN --- NC    = ON



#15 RestoLynx OFFLINE  

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Posted Thu May 11, 2017 2:53 AM

Thanks for the reply I didn't have the EN connected to ground :) .

 

Perhaps I should forget about using the 9v side in the Lynx and just put the powerboost straight into the 5V side of the circuit, across C41; this would eliminate the voltage losses. I think the only downside is that I lose the On|Off button functionality (the reason I started this thread!), but I can hack something together using the EN pins and a switch or re-purpose the existing On|Off buttons. Thoughts?


Edited by RestoLynx, Thu May 11, 2017 2:55 AM.


#16 af0l OFFLINE  

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Posted Thu May 11, 2017 3:55 AM

Correct. 9V is a silent killer, like high blood pressure. It's fine - until it isn't.

 

If I ever get my father to actually produce the circuit for on/off, I can make a small run of them for those interested...



#17 RestoLynx OFFLINE  

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Posted Fri May 12, 2017 2:33 AM

Done and working perfectly!! 5V across C41 and it is running well. At the moment I' switching it off by connecting the EN to GND (see below), I'll put in a switch in a while. As an aside; I measured voltage across C41 when i was putting 5V into the 9V side, and it was 4.6V.

 

y8HdDzSl.jpg

 

fEdlsmrl.jpg



#18 af0l OFFLINE  

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Posted Fri May 12, 2017 2:38 AM

Splendid!

 

Meanwhile I talked to my old man - he is prepared to do the design and prepere the pcb with simple on-off logic. Would you be interested in that? I should probably start a poll or sometning to see how many of us would need this, so we can have it made in a single run...



#19 RestoLynx OFFLINE  

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Posted Fri May 12, 2017 2:52 AM

I'd be interested, but you are looking at a very small subset of people who have upgraded their Lynxs! 

 

(For people looking at this thread in the future : The batteries I used were two 18650s from a drill battery pack, running in parallel)



#20 af0l OFFLINE  

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Posted Fri May 12, 2017 3:35 AM

Well, I have three of them... :)

 

 

It hould also be a simple thing (as you can see form a schematics above). Maybe if we just get the resistor values correct, people can make their own.



#21 cowdog360 OFFLINE  

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Posted Fri May 19, 2017 4:48 PM

I'll also talk to my engineer buddy. Maybe we can just have one board that has charging, boost and power latch.

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#22 af0l OFFLINE  

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Posted Sat May 20, 2017 4:59 AM

Yep, I thought of that too... Talked to father about it, but he wasn't too enthustiastic about it - the price/preformance of the Poweboost is hard to beat at these volumes...






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