I just got the DSO nano (by the way, very nice project!), but I almost immediately went into a couple of issues:
first, apparently the device doesn’t work as usb storage, both under windows XP and linux. I followed all your instructions on getting the sd card working, but I had to use an external usb reader to do it. when I connect the DSO to a computer with an USB cable, I get errors: XP asks to format the device, while linux gives read errors and doesn’t recognize the partition. in both cases if I reformat/repartition the card, using fat16 and putting the necessary files on it, I obtain an “SD card err” on the dso.
this is not a great issue, just I have to remove the card to access it, but it would be nice to use the DSO as external storage: just added value to the product!
a more substantial issue comes from the battery: I connected it, fully charged and then discharged to test duration (something between 2 and 3 hours), then charged it again. the problem is the following:
the battery icon after the device is turned on shows immediately “battery low” (yellow)
if the device is left off for a long time (hours, but I have to test to get a more precise value), then it will turn on only if connected to an usb cable. when the cable is connected the device turns on immediately and stays on for a long time even if the cable is removed, so it is not just a battery problem
I hope these problems con be fixed with a firmware upgrade, anyway thanks in advance!
first , the STM32 most resources be used to do the measure and to calculate , so if you use the DSO Nano as card reader to modify the card via the usb , then it’s very slow, and it may be timeout for some computer USB, and we don’t ensure you can use it to dify or fomat the card. we suggest you to fomat the card and add the file ues the external card reader .
the battery measure bug is still the problem , it can be fix by the firmware. we must to test the battery discharge curve, and choose some point for DSO Nano to adjust the battery state.
now the battery display is not very accurate, especially when battery in the low power state , the voltage is not stable so the DSO Nano may make some mistake.
About the battery problem, after some new tests, I found that the problem may be actually due to a faulty battery or charging circuit: after a full charge and leaving the DSO off overnight, it turned on correctly the morning after. anyway, the battery icon changes to nearly empty (yellow) in few seconds. So it is possible that:
the battery is faulty and self discharges, so even with the instrument sitting unused id depletes and after some time it will not turn on
the charging circuit does not charge properly the battery so it stays permanently in an almost empty state
if it can help, for the usb storage issue, i’m attaching the entries in the logs of my linux laptop that are displayed when I connect the DSO… dmesg.out.gz (886 Bytes)
actually, after a 6-hour charge yesterday evening, this morning the dso has turned on but the battery lasted just 5-10 minutes, so I can reduce my hypotheses to these two:
as said in a previous post, the battery level reading is wrong, so the charging circuit stops charging too early
the battery is faulty and does not take the charge
Considering what has been said, I would take te first of the two, that is also the better (it fixes with a firmware upgrade…)
I’ll wait for new updates! (in the meantime I’ll try to make a tool to extract a time/voltage ascii file from the saved waveforms)
well, I charged the DSO while it was off: from the schematic in the manual it seems that the charging circuit is connected directly to the usb, before the on/off switch, so I thought it was the same (or better, it would charge faster without the power consumption of the instrument operation…)
anyway now the DSO is turning on correctly even after several hours of being off, so actually the problem is only the battery charge level, probably the first time I charged it (3-4 hours), the battery level after the charge was so low that it wouldn’t even turn on. after that i made a couple of cycles (charging several hours and discharging) and the things apparently got a little bit better
anyway, now even leaving the usb cable connected for a whole day, when I remove it in a few seconds the battery status goes again to low. I suppose that the problem is in the battery voltage readout. probably the charger reads a “full” value too early and stops charging.
Note: when the instrument turns off, I saw that the lcd backlight fades, so actually what causes the shutdown is really the battery going depleted, and not a wrong reading of the battery voltage (driving a software shutdown…)
I hope it helps… (and wait for a firmware upgrade!)
If you look at the sch that you will see the charger IC is be short circuit by a diode, so now when you connect it to USB(shut off) then the battery will be connect to the USB VBUS~ then the 5V-0.7V=4.3 V voltage direct charge the battery~ it’s not a good idea to do so, because this way cannot charge the battery to wholely full , but if we move away the diode , that the charger IC work~ you can charger the battery to full , but what you lost: you can not just use the USB power without battery~!
now i have used one battery to test ~ i have been using it half a day and now its voltage goes down to 2.9V so the DSO Nano considers that it’s low power and cannot be turned on now. and i will charger it for 6 houres that you try to test how many energy can be charger into it , but now just 1 hour it seen the voltage go back to 3.95V ~ and jsut see can it full up to more than 4V , and i will test how long can it work again … if it work naturally , that may be the battery that you use is bad …
good! now I’ll try to charge the DSO for some hours while ON: if it works (battery full, and stays full even after a couple of minutes) all is working correctly
on the other side, if the battery level does the same thing (turns to low after few seconds), means that the battery is bad…
It seems that the USB VBus cannot charger the battery fully, and the highest votage is about 3.95V , but this battery can use agian without usb mord than two hours …
ok, you’re right, if you charge the device while on, the results are consistent, the battery indicator show a reasonable “almost full” green icon that stays there even after some time. it just need to be charged while turned on… not a big issue anyway
by the way, a question: I couldn’t monitor directly battery voltage since I have closed the DSO and don’t want to try to open it again, but is the internal oscillator amplitude related to battery voltage? it appears so to me… about 3.6-3.7 volts when operating on battery, and more when charging…
I checked the difference between charging while on or off, and actually doesn’t matter. the differences I’ve seen are most probably due to differences in voltage (used different PC and also an external USB charger).
using the same consistent supply (macbook usb), I get a consistent 5-10 min of operating time with 5-10 hours of charge!
very sorry of this, if it wasn’t for the battery life I’d have pre-ordered another one or two for my lab!
let me know if you come out with a soultion, the only one I have is to use a different power supply with slightly higher voltage, but it’s risky and not convenient, the nice thing in usb devices is just that you do not need an external charger
thanks for your suggest~ we will try using the MAC to charge the DSO , we just use the X200 to check and the battery can be use more than 2 hours after 90 min charging.
we will use the new charge circuit and change the battery , and will test the using time and the charge time of the battery .
the issue with the charger circuit can be solved easily and cheaply without too many compromises . Here is the circuit:
Transistor act as a diode here. And it is connected backwards on purpose. Model selected was price driven (0,125€ ~ $0.186) and gate voltage must be lower than the minimum battery voltage (important). This model has an Vg of -1.5V.
By the way, dropout depends on MOS resistance and current consumption. This MOS has a resistance of [email protected] and that translates in a dropout of 52mV@100mA.
If you have any questions regarding how the circuit works feel free to ask.
The FET will only act as a diode until it is turned on. Once the FET is turned on, it will conduct in either direction, and you won’t be able to turn it off. So, as drawn, the FET is a resistor, and won’t do what you intended, which is for it to be a diode.
If instead you put a resistor in between the gate and ground, and a resistor from the USB input to the gate, then the FET would turn off when the USB cable was plugged in, which would do what you wanted.
No R25 will not work for this purpose. The pullup resistor needs to be smaller than the pulldown resistor, or there will not be sufficient gate voltage to turn the FET off, so another two resistors will be required.
