AVR Freaks

Thanks for the replies.

I'm not committed to anything, as yet. I've only got a prospective schematic drawn up, so everything is quite fluid at this time. The major requirement for this project is size. The PCB needs to be 1" x 1.5" x 0.5". So everything must fit in this area, minus the motor ans pressure sensor, and it must be realized with a single-sided PCB - by client requirements.

I'm not so much interested in the technology of measuring the motor current, as I am the technique. I was hoping that I could measure the real time motor current while the power was actively being applied, and not an average form of it. This part is not a customer requirement, but a matter of my own experiment and learning experience.

As I have posted in the past, I had been developing a closed-loop servo motor controller some months back that was shelved for other priorities. I was hoping to use this new project to gain some insight as to whether or not I can measure instantaneous (PWM cycle by PWM cycle) motor current and apply my findings to the closed-loop servo motor controller that I hope to pick back up very soon.

Again, thanks for your input.

Nard,

The acronym "SMPS " eludes my understanding. I don't (or cant reason out) what this means.

But the motor is specified at 12VDC @ 0.3 Amperes. It's certainly not a sizable motor at all, compared to say, 5, 10 or even 20 Ampere motors that I've worked with in the past. And all of those were open loop and used no type of current monitoring - simply blind control - save the closed loop system that I've been working on, targeted at my Table-Top mill. .

While this clients needs does not require closed loop, nor is there any specific request for current monitoring/limiting, I'd like to at least add some protection, as it is supposedly being designed to perform some sort of critical control of an industrial "Something-or-Other " requiring corrective response from the device I'm designing.

The specification from the client are adequate to build his specific requirements. I just don't think he's thought through anything having to do with fault notification and any possible corrective action that could be required.

Other then what I've already explained above, I have not been told what the actual end application is. I've only been told that I need to design a control that starts a small pump that will run for up to 5 minutes when triggered into operation by a pressure sensor that is monitoring the differential pressure of some sort of exhaust blower.

EDIT:
Design specifications:
1. The controller will operate directly off of a 3V3 lithium coin (CR2032) battery.
2. The design needs to operate for at least 30 days, from a single battery.
3. Battery replacement at 30 days is a scheduled maintenance activity.
4. The pump motor will be powered from a secondary 12VDC power source.
5. The design will start a pump motor when triggered by the actuation of a differential pressure switch.
6. The pump motor will run for a maximum of 5 minutes.
7. The trigger is edge sensitive - meaning that the pump motor will come on only when the blower motor initially starts, and when the 5 minutes have timed out, the pump motor will turn off - and remain off until the blower goes through a complete turn-off and turn-on cycle.
8. The design must have a watch-Dog that ensures that the pump motor turns off within the given time interval - precluding the use of a simple NE555 timer for the On-Time control for this project.
9. The design must have a "Device Operational " indicator in the form of a pulsing LED at 5 to 10 second intervals - also precluding the use of an NE555 timer.

True, this could be accomplished with a couple of NE555 timers, but a Mega48/88/168 controller will cover all of the requirements, with a tremendous room for expansion.

I've posted a schematic of what I've discussed.

I tried to post the attachment using 640x480 resolution, but the detail looked like crap. Sorry for the excessive size.
The final component values have not been fully decided upon, as of yet.

Comments welcome.

EDIT:
Update schematic to reflect suggestions.

EDIT:
One more time...

Ah, yes! Isn't that an interesting mistake I missed? I added the sense resistor later in the design, and then forgot to move the 12VDC common.

The schematic has been updated for the LED current limiting resistor, as well as the 12VDC common reference.

Thanks guys!

I finally got a PCB made and assembled. I was also able to setup the fuses on the first try.

I'm running a Mega168 on the internal oscillator/8, on a 3.0 volt CR2032 coin battery.

The small traces are 0.01" and the larger traces are 0.025". The PCB dimensions are 1.45" x 1.75".

Pictures are attached...

Check-out and test programming will begin tomorrow evening.

I've added some extras onto this PCB. So after the functionality is codded, I'll be experimenting with adjustable current limiting.

But I'm sitting here rationalizing out the coding that I'll be doing over the next few days, and the basic operation is actually quite trivial - an input goes low, the motor starts and runs for 5 minutes, then shuts off. If the input remains continuously low for say, a 30 minute period, the motor re-starts and runs for another 5 minutes. The cycle repeats endlessly.

But the part that I'm having trouble getting up to speed on, is putting the thing to sleep and waking it up once a second to check the input and service the output. I've not done any work with any of the sleep modes, as yet. So I'm still a little intimidated by what might need to be done, and what I haven't though about yet. But I definitely need the sleep mode, if I'm going to get this thing to operate for 30 day periods between the scheduled maintenance events.

Oh well, like everything else, I'll figure it out - but it'll probably when I'm pushing a walker.

Thanks for the complement, Doc.