Steve's Junk » pic18f2620

Viscometer Ver.(Eleventy Billion Jillion) a la rotational

smackaay — Tue, 03 Mar 2009 06:40:14 +0000

Well, this has a been a long few days of work. I have created the ideal rotary viscometer in both terms of price and repeatability. Now, this idea is nothing new but I’m simply happy that it works. I guess it’d be prudent to go in to how it works…

How it works:

The concept is simple. you have a shaft that is separated by a spring, in this case two plastic cups connected by a ball bearing with rods sticking out one side. This shaft is driven by a small gear motor and a set of paddles is attached to the other end. While this is rotating, the difference in the driven and the resisted side is measured with some form of instrument be it a hall effect sensor or a slot type optical transducer.

Viscometer and stand

What I used:

Well, as far as materials are concerned, for the prototype I used blocks of polyethylene to support both the motor and the shafts. The material has pretty low friction properties at low loads and thus I used it as the bearing on the bottom. The actual difference mechanism is made from a high density plastic. I would probably use this material again as it’s light, rugged and easy to machine. For the real unit, I may still use this plastic as it is more than strong enough and it’s easy to machine.

As for the drive I used a design similar to the older designs with PWM motor output, serial output, keyboard input, LCD out and 2 channels of input. This is all controlled with a PIC18F2620 which is more than enough for it’s needs.

The motor itself is a Hsiang Neng gearmotor running at 12 volts. It’s a piece of shit but that’s not important at this stage of the game.

Motor and sensor

So, finally, a desired feature list:

1. RS-485 Out
2. KU and Cp out
3. Multi-fluid calibration, this feature allows the user to select fluids of any KU value and calibrate the unit by entering them in.
4. Easy to use menus. Too often have I seen automation stuff that’s unintuitive. This hould be easy for the operator to understand and easy for the people to use.
5. Speed selection, so that you can use under-powered motors.

Anyways, here’s a gallery of some of the pictures of what could be a DIY stormer viscometer.

Sky-Tracker, so far, so good.

smackaay — Mon, 09 Feb 2009 23:07:24 +0000

For the last few days I’ve been working on the electrical portion of an astrophotography mount for my camera. The mechanical portions were built by my father and I’m handling the electronic portion of the device. Basically, for those who don’t know, this device is designed to allow one to take long exposures of the stars without them blurring due to them moving across the sky. This device moves the camera in such a way that allows for said movement.

Originally, my father and I spent a day working on both the frame and the electronic portions of the unit. I quickly whipped one up with a protoboard I had laying around and a PIC16F690. I used an SN754410NE H-Bridge driver for this design as well. Unfortunately we didn’t finish the project that day, and I wasn’t keen on programming the PIC having to pull it out of the IC socket every time I wanted to test it.

The original defunct board. This board was omitted due to the fact that it had no ICSP provisions.

Anyways, many months have passed since then so I decided to finish ‘er up. This time though I wanted the underlying design to be flexible enough to handle any configuration of “barn door” and to allow for nice methods for both calibrating and homing the device, whereas most DIY methods are rudimentary at best. The reason I want to make it more robust than needed is due to the fact that I believe that a nicely finished electronics board kit may sell quite well, or perhaps even the entire unit if done in a low-cost, high quality way.
Here are some of the planned features:
1. Multiple configurations built-in for both screw pitch, motor step angle and “barn door” configuration
2. Homing and End Range Switch provisions to allow for homing of the device and mechanical damage prevention.
3. Support for 12 and 16 button keypads.
4. Support for 8×1 or 16×1 HD44780 LCD displays. I choose these because they’re cheap and formatting for this style guarantees compatibility.
5. Multiple drive options, Full-step, Half-Step, Strong movement, weak movement.
.
Anyways, Here are some images and descriptions of how I put it together, up till now. As of this writing, it’s not finished yet. It will take some time methinks.

First, I took some Stripboard and planned out the pinouts and connections. Stripboard (or veroboard) is my favorite since it’s so damned easy to plan. Despite there being a great many other protoboards out there, veroboard has been the most useful, for me anyways.

Planning it out

Starting the board

Halfway done

Board pretty much complete

.
There were a few kinks to work out but not many, despite how messy this board is.
It took me a while but I got the keypad, LCD and Stepper running. It didn’t take very long for the LCD and keypad since I’d already developed my own libraries for those functions. I then played with the stepper motor and got it working.

Astrophotography electrics working with keypad, LCD and stepper motor

.
Now, to mount it in the enclosure. I just happened to have an ideal enclosure and a sealed lead acid battery from princess auto. The battery charged fine and I think it will serve quite well to run the stepper (This motor draws about 200-400ma depending on drive configuration). Here’s what it looks like as of today.

Electrics in Enclosure

I’ll have to give the enclosure some rubber feet since the mounting screws jut from the bottom but that’s cosmetic at this point.

Anyways, I’ll report further progress, as usual, on my blog here.

Here are some interesting links
http://www.keteu.org/~haunma/proj/barndoor/
http://www.cs.uiowa.edu/~jones/step/types.html

Comment if you wish.

Working on yet another stormer viscometer board. :(

smackaay — Mon, 27 Oct 2008 20:50:15 +0000

Well, For the last week or so I’ve been developing a new viscometer board. Sloppy as it is, it’s a jump ahead from the last board in terms of overall inputs allowed. I used the 68PLCC package PIC18F6680 in this one because it had a sufficient number of IO and because it looks cool in it’s socket.

Anyways, this one has the following features:

Several analog channels for temperature measurement.
Several analog channels for use in a torque sensor set-up.
Some analog channels.
built in RS-232 Output.
built in RS-485 Output.
Provisions for PICKit2 hookup.
TVS’s on all input lines
Separate PIC12F683 for PWM output
Debug Serial Output.

All in all, it’s gone smoothly, I’ve double checked a number of the traces, let’s hope all of them are well when they come back from AP Circuits later on.

: Yet another iteration of the stormer viscometer board