Problem running 08m2 at low voltage

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Haku

Senior Member
My wireless Xbox controller has a habit of turning off if I leave it too long, and online games kick you off if you idle too long, so I wired an 08m2 into it to 'press' a button every minute to stop the controller turning off and stop the game from kicking me out.

One small problem, I use 2x rechargeable AA's in the controller and first attempt at programming the 08m2 when powered from the controller didn't work, the batteries were reading 2.2v, I put some just charged ones in that gave out 2.8v and the 08m2 programmed fine.

I tried 2 different 08m2's and neither would program or run the code at 2.2v but worked fine at 2.8v.

I thought these chips were supposed to run as low as 1.8v? Why wouldn't it work?
 
A

AllyCat

Senior Member
Hi,

No, the minimum Vdd rating of the 08M2 is higher than 14M2 and 20M2 (which are ~1.8 volts).

In my experience 08M2s just about work down to ~2.2 volts and even using DISABLEBOD doesn't help much, if at all. :(

Cheers, Alan.
 
Hemi345

Hemi345

Senior Member
Probably because he's using the two batteries already built into the game controller.

The MCP16251 or MCP1640 could boost the voltage to 3.3V with minimal additional parts (tiny inductor, two resistors for Vfeedback, and decoupling caps).
 
A

AllyCat

Senior Member
Hi,

Or use rechargeables: 2 x NiZn (1.6v per cell) or 1 x LiFePO4 (Lithium Iron Phosphate - 3.2 v per cell - NOT the normal Lithium type), the latter with a dummy (short-circuit) "placeholder" cell in the second battery bay. Both types available in AA style in the UK, but larger capacity (and cheaper) LiFePO4s mainly from China via ebay.

Cheers, Alan.
 
G

geoff07

Senior Member
There is another way ...

Years ago I had some responsibilities for IT in a certain company, and we had DEC AllInOne as an email system for one division (that tells you how long ago it was).

Due to limited resources on the VAX host, AllInOne kicked users off if they were idle for a certain time. This irritated one user so much that he made a solenoid-operated mechanical finger that pressed the return key at intervals to stop the timeouts. He was discovered because of the perplexingly huge number of page faults that his userid was generating compared to anyone else.
 
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Peter Graat

New Member
Hi, just a thought. Is it possible that for programming the flash of the µC (so programming) that you need a somewhat higher voltage like approx. 3 Volt. After programming the voltage of just running the µC could be lower?
 
H

Haku

Senior Member
Peter Graat said:
Hi, just a thought. Is it possible that for programming the flash of the µC (so programming) that you need a somewhat higher voltage like approx. 3 Volt. After programming the voltage of just running the µC could be lower?
Click to expand...
Sadly that doesn't work either, I tried programming it with freshly charged batteries and made sure it worked, then swapped over the lower voltage batteries, the Picaxe wouldn't run.
 
A

AllyCat

Senior Member
Hi,

Did you try DISABLEBOD (Brown-Out Detector)? However, it didn't help me much with an 08M2. :(

Also, bear in mind that the Programming process uses verification/handshaking, so the PICaxe Serial Out Interface must work correctly. It should be fine with TTL levels (as used by the PICaxe programming cable), but if you happen to be using an RS232 "COM" port interface, then signal levels of 0 and +2 volts might not be enough when it's "expecting" levels of (up to) -15 and +15 volts. ;)

Cheers, Alan.
 
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