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Automated Solar Powered Horizontal Blind Controller
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not sure. Ofcourse if there still is a a pwm command active that explains the voltage.But then it shldnt make any difference whether u use PNP or NPN down the line.Anyway, it works for you and that is good
I'm sorry - I said that wrong. I measured a slope from 5V towards 0V on the PWM pin, NOT the base pin. So I measured voltage going BACK to the Arduino.The successful low-side switch configurations I've seen all used a 2-wire motor or device. Since the servo is a 3-wire device, could that be the difference?
given the fact that you have an active wifi signal, it might be a challenge to feed it off a battery, but yes would love to see that too.@froz3nArcher. If you have size considerations (like for building it into yr blinds) the 8266-01 is the smallest and you still have 4 I/O pins. If you have good eyes and a steady hand then pin 14 is also 'easily' made available.Frankly, the ESP8266 is a great device
that was my fear too
That is odd, cant think of any reason for it. I use low side switching with an NPN to switch voltage on a soil moisture measuring pin (to avoid excess corrosion) and that switches it off completely (as far as I could measure).I think I used an old VP140 transistor for thatAnyway, it was just a suggestion, stick to whatever works for you :-)
Thanks for the feedback! I was afraid of this, too, but tested and worked OK, driving a small servo. May depend on the application.
The third one is the Lithium battery charging module. Part number 10 in the list.
In discussing this with a friend who has an electrical background, he thought the diode would interfere with the PWM signal. That'd be something to try to see if it's true.
I tried more than one NPN and got the same results. I don't think it was a bad transistor however, as I wasn't getting voltage on the emitter pin - I was able to measure voltage (decreasing over time) on the base pin. As in, it started at 5V during execution, and while sleeping slowly crept towards 0V over the course of several seconds. I didn't like that, couldn't explain it, but it felt wrong. Was able to eliminate that issue using the PNP high-side.
you could be totally correct. I havent tried that. it may vary per motor and maybe also makes a difference what motor one uses and whether the signal pin is HIGH or LOW. Not sure if a diode would interfere with the PWM signal
low side switching with npn is possible, zero consumption, BUT you need a diode on the signal wire of the servo, otherwise the servo pin on the arduino drains some current.
you use 3 pcb-s. one is the pro mini, one is the 5v dc-dc, what is the 3rd one?
Thanks. True, the emitterfollower us rare for such use, that is why I initially hsitated too. I am using an emitter follower to switch current to moisture pins and there is no current when it is OFF.Now technically, if it were just a traditional low side switch NPN (load in the collector) as you tried, if configured ciorrect also shldnt have any current flowing when off, but transistors are not always ideal switches, maybe your transistor was not up to spec or maybe there was something else as you already suggested. Main thing is it works
Thanks! Everything done in this instructable (well, the previous one) was a new skill for me, minus the software. You are correct regarding the PNP and NPN configurations I tried. I did try an NPN in an emitter follower circuit, but everything I read seemed to indicate it was rare. Not knowing why it was rare, I figured I'd stay with a more traditional use of the transistors. I didn't measure down to the sub-mA level when I tried it, sadly. At the mA level, it was the same current, but what you say makes sense - it seems like it should be lower.I've looked at some of your other projects, I like what you've done with the attinys. Seems like a good way to reduce current even further.
If you do that, I'd love to see it, and hear what your sleep/idle current is. Part of the challenge of this was reducing the battery usage in order to handle several days of overcast. I don't have an ESP8266, so can't measure it. I should just go get one.
It would be pretty simple to replace the arduino with an ESP8266 and make it controllable by wifi. I am thinking this would make an excellent OpenHAB system addition. Thanks for the write up! - armorer243
Great instructable. always wanted to do something like that but always stranded on the mechanical side of it :-)High Side switching with a PNP transistor I presume takes a high on the base to switch off the motor. Although that will likely be much less than the 13 mA of the servo it still will cost some current.You tried Low Side switching with an NPN, I presume having the motor in the collectorline. You may try high side switching with an NPN (yes, an emitter follower circuit) that will take less current in rest (pin Low) and may alleviate yr earlier problem - diy_bloke
Great instructable. always wanted to do something like that but always stranded on the mechanical side of it :-)High Side switching with a PNP transistor I presume takes a high on the base to switch off the motor. Although that will likely be much less than the 13 mA of the servo it still will cost some current.I presume high side switching with an NPN (yes, an emitter follower circuit) will take less current in rest - diy_bloke
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