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Forum Index : Microcontroller and PC projects : Micromite CPU SLEEP
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
I am sure this has been discussed some time before but can some remind this GHOB (grey haired old b) how I can recover from this predicament: Micromite 150 running 4.5E Have edited the program to reduce power consumption with CPU SLEEP 1000 and AUTORUN is implemented. So as this was not available until 5.1 can I break the program without having to re-program the chip? GM |
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robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2294 |
shorting together TxD and RxD while applying power will do a factory reset. you could also try feeding the output from a signal generator into WAKEUP and hold down ctrl-C on your terminal and see if you can break out of the loop. cheers, rob :-) |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Thanks Rob, but as it would be the case I have not saved the code so a rx/tx short will loose the programming. |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Success!!!!!!!!!!!!!!!!!! Thanks Rob for reminding me. A ground on the reset pin combined with a CTRL-C did the trick. Wonder what I can stuff up next. GM |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
I changed the 150 to 170 with 5.1 and issued the cpu sleep 3 in the program but the circuit still draws 4mA during the sleep period not the 80uA as suggested in the manual. I have stripped down the circuit to try and find where the current draw is. along with the 170 chip is a 100k/10k voltage divider to an analog pin, a LED via a 100R resistor unlit and the 3T 3V3 regulator. Could the current draw be an overhead of the 3T regulator? Any suggestions? |
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robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2294 |
what is the part number of the regulator? 4mA sounds about what i'd expect, assuming the regulator is nothing special. |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Rob the regulator I am using is the L78L33ACZ dropping 5V to 3V3. GM |
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Geoffg Guru Joined: 06/06/2011 Location: AustraliaPosts: 3167 |
Reducing the current drawn in sleep can be difficult. Any I/Os will continue to draw or source current so they should be disabled if you suspect that. Also, peripherals like the serial UART and SPI will draw current in sleep if they are open. You can test the sleep current of the bare chip with nothing connected to its I/Os by running a program consisting of just the command CPU SLEEP. Geoff Geoff Graham - http://geoffg.net |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Thanks for the input Geoff. I will strip out the program and report back with a measurement when I am back in the shed tomorrow. GM |
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robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2294 |
according to page 6 of the datasheet here: http://www.st.com/web/en/resource/technical/document/datasheet/CD00000446.pdf the quiescent current is no more than 6mA. this would seem to be the likely offender! do you need to have a regulator at all? a micromite should be happy on a pair of AA cells directly. cheers, rob :-) |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Rob, In this case the micromite is monitoring a 12 volt battery so that is why I would like it to draw as little current as possible. On the bench I am only feeding it with 5v from the USB-serial converter. |
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robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2294 |
you may wish to consider the LP2950-3.3 in that case, with a ground current of 120uA or less under light loads (according to the TI datasheet): http://www.ebay.com/itm/181847005970 http://www.ti.com/lit/ds/symlink/lp2950-n.pdf cheers, rob :-) |
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WhiteWizzard Guru Joined: 05/04/2013 Location: United KingdomPosts: 2794 |
I like to use the MCP1700 3v3 LDO for MicroMite circuits that 'sleep'. They draw just 2uA so are ideal for battery circuits with the occasional 'processing' time. Also conssider reducing CPU speed to as low as possible (but remember that some commands require a higher CPU speed). WW For everything Micromite visit micromite.org Direct Email: whitewizzard@micromite.o |
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robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2294 |
unfortunately the MCP1700 range of regulators have a maximum input of 6v according to this datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/20001826C.pdf cheers, rob :-) |
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paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
The MCP1702-3302E (TO92) is supposed to be good for 13.2v input and the MCP1703-3302E/DB good for 16v input in the 4pin SOT223 package. |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
I see that Jaycar has the LM2936 3.3v reg in their list. Would you think that that would be a good contender? GM |
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robert.rozee Guru Joined: 31/12/2012 Location: New ZealandPosts: 2294 |
the LM2936 datasheet lists: ±2% Initial Output Tolerance ±3% Output Tolerance Over Line, Load, and Temperature http://www.ti.com/lit/ds/symlink/lm2936.pdf while the LP2950 datasheet claims "a tight initial tolerance (0.5% typ), extremely good load and line regulation (.05% typ) and a very low output voltage temperature coefficient, making the part useful as a low-power voltage reference". given that the micromite uses the 3v3 supply as the analog reference, and that your application is making use of the analog inputs, the LP2950 would still seem to be the preferred choice. i trust you are ok with ordering parts from ebay? it is extremely painless, you use paypal for payment - with a credit card you can use a guest paypal login. the whole process is extremely safe and takes just a minute or two to complete. cheers, rob :-) |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
Thanks Rob, I am OK with ebay ordering and have accounts with RS and Element14 just a bit impatient. GM |
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OA47 Guru Joined: 11/04/2012 Location: AustraliaPosts: 911 |
It has taken some time to get back to it but the 170 chip in sleep mode draws a whopping 56uA. I have set the 170 chip to flash a high brightness LED for 1mS every second running on a 2032 button battery. It will be interesting to see how long it lasts. GM |
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