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I’ve set out to build a Prusa Mendel for $300. So far I think I’m doing pretty well. The top part is what I’ve already picked up, and the bottom part is what I have yet to purchase — that’s where I still have some flexibility in cost. The first column is the percentage of total cost for that part. Shipping charges for a group of items from the same supplier are listed with the first item in that group.
By the way, I fully expect there to be some mistakes in here — I just hope they’re not on the most expensive parts. In fact I’ve already made a couple. For example, I ordered nylock #6 nuts instead of regular ones. In cases like these, I’ve just corrected the prices.
It’s not easy to find concrete examples of shipping costs for McMaster-Carr online, and they don’t tell you what an order is going to cost to ship until after it’s already shipped — and that can be a little scary especially if you’re ordering odd sized parts, even if they only charge their shipping cost. So here’s a real example of shipping costs for a small order with some long parts to NC, USA. The order was placed online and shipped the same day from their Atlanta, GA, USA location.
For a reprap build, I ordered these items, which include three 3-foot steel rods, 200 nuts, 292 washers, and 200 machine screws. Shipping was only $6.52 for everything. That’s not bad at all…
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Well, I discovered that Popsicle is a brand name, so I’m officially renaming this little guy “StickBot” so the Popsicle police don’t come after me. To be clear, this little bot has nothing to do with Popsicle brand ice pops, and never did. My appologies Popsicle; I hope you still let me eat your ice pops because life just would not be the same without them.
Now that I’ve come clean, here’s a video that show how to assemble StickBot’s right eye. It’s an analog 555 timer-based 1Hz oscillator that controls the right/left PWM servo signals generated by the left eye.
This is the latest version, powered directly by four 1.5V LR61 batteries (similar to AAAA batteries, and often found inside 9V batteries). As a result, it does away with the voltage regulator.
Details for the previous version can be found here: StickBot V2.0 - Untethered!. The original tethered version can be found here: StickBot: A Simple 6-Legged Walker. I’ll try to get updated schematics and more assembly videos up soon.
I’ve had a few people ask me if I have a kit for this little critter. I’m working on one geared toward kids — it’s a fun project to do with kids, and it seems like they really learn a lot from it.
The parts for this eye include:
- 555 Timer IC
- 1k ohm resistor
- 330k ohm resistor
- 2.2uF capacitor
- About 9 inches of Cat 5 network cable, phone cord, or other similar wire
- Some electrical tape, solder, and soldering iron
Here’s a video of my very hackable 12-channel logic level shifter/translator with a voltage regulator. This video demonstrates how it works. There’s more detail here at the DIY 12-Channel Bidirectional Logic Level Shifter post.
In this example, it’s translating from 7.5V to 3.3V. In another example at the link above, I’ve demonstrated the hackability by wiring it up to drive a 3.3V Nokia 5110 LCD, using five of the 12 channels as logic level translators. Channel two is wired directly to 3.3V for power, channel three is wired directly to ground, and the transistor on channel nine is turned so that the 5V signal controls the gate, which allows PWM control of the LED with full power from the regulator.
Music: “Art Now” by AlexBeroza (CC BY 3.0)
40-pin female headers are inexpensive and easy to trim down to size, and with a dot of CA glue (super glue), you can even easily make other configurations, like 2×4. Sometimes they’re even described as “break-away” headers, although admittedly they don’t break away as easily as the male pin headers. Just keep in mind that if you don’t score it, it could shatter.
Someone was looking at one of my PCBs and commented that it’s “impossible to break them apart without destroying at least 2-3 pins each time.” Using this technique, I’ve never “destroyed” any more than one, and with a little care, the edges turn out quite nicely.
Music: “The New Music” by AlexBeroza (CC BY 3.0)
He we’re test-driving the our latest robot creation for the first time. It’s the boy’s design and made mostly of wood. The tires are o-rings, and there’s a 12V AA batter pack sandwiched between the two pieces of plywood. The system right now consists of a drive controller using a Modern Device‘s RBBB (small Arduino-compatible) and the Pololu TB6612FNG Dual Motor Driver Carrier, a robot controller, which is a standard Arduino Uno (which doesn’t do a whole lot right now expect forward messages from the remote), and a remote controller, which is another RBBB, joystick and display.
Right now there are two driving modes. The first is a tank drive, where, for example, if the joystick is moved far left, the right wheel moves forward at full speed and the left week backward at full speed. The second mode is what I call “target drive,” in which you set the target speed and direction of each wheel. Soft starting and stopping is built in to the controller, and the jerkiness you see sometimes is a bug in the keep-alive timer — if the robot stops getting messages in target drive mode, then it will stop.
Music is “Don’t you” by stefsax (CC BY 2.5).
Here’s a 12-channel bidirectional logic level shifter with a 3.3V power regulator that I designed so I could easily interface 5V circuits with cool 3.3V widgets like the ADXL345 accelerometer, the NRF24L01+ wireless transceiver, and the Nokia 5110 84×48 LCD. For the one in the picture, I used round machine pin headers because I use it with hookup wire and those female headers are very easy to separate from 40-pin lengths.
DIY 12-channel Bidirectional Logic Level Shifter / Logic Level Translator, using AMS1117 and 2N7000 MOSFET pass transistor interfaces
Up to twelve 5-15V logic signals can go into one side and come out as 3.3V signals on the other side, or the other way around (3.3V signals go in and can be read as 5-15V signals) in any combination. The regulator portion converts 5 to 15V DC into a steady 3.3V for up to 1 amp.
In this video, I show how it works translating from 7.5V to 3.3V. The video is from the A Hackable 12-Channel Bidirectional Logic Level Shifter/Translator post.
Why did I not just use a 74HC4050 or some other logic level translator? Because this is much cooler! It’s bidirectional, it has twelve independent channels, in includes a 3.3V regulator, it’s inexpensive, it’s good soldering practice, and it’s hackable. In the photo below, I’ve wired it up to specifically drive a 3.3V Nokia 5110 LCD. It uses only five of the 12 channels as logic level translators, channel two is wired directly to 3.3V for power, and channel 3 is wired directly to ground. The transistor on channel nine is turned so that the 5V signal controls the gate, which allows PWM control of the LED with full power from the regulator. I’ve also used a different resistor. (More photos below.) And why no resistor arrays? Because resistors are usually inexpensive and on hand, and resistor arrays would limit hackability.
Logic Level Shifter Hacked for Nokia 5110 LCD
It’s essentially a AMS1117 3.3V regulator with capacitor at the top, and then an array of MOSFET pass transistor interfaces with n-channel 2N7000 MOSFETs. Each side is held high by a resistor 5.6k ohm resistor. If the 5V side is pulled low, the voltage from ground to source will be 2.7V because the diode becomes forward biased, and this turns on the transistor, pulling the 3.3V side low. If the 3.3V side is pulled low, the transistor also turns on with 3.3V, pulling the 5.5V side low.
It was designed using KiCAD (free), and PCBs were ordered through SeeedStudio’s Fusion PCB service. All the components are easily available online, at Digikey or on eBay. Here are the parts I used. The costs reflect per items costs for small bulk purchases (usually around 10-50 pieces) on eBay.
- 1 AMS1117 3.3V 1A Voltage Regulator – 28¢ (datasheet)
- 1 22uF electrolytic capacitor – 9¢
- 12 2N7000 n-channel MOSFET – 60¢ for 12 (datasheet)
- 24 5.6K ohm resistors – 43¢ for 24
- 2 12-pin female headers (I used round ones for the one in the picture, but you should use the standard square ones if you’re not just using jumper wires.) – 29¢ for one 40-pin header, then cut into smaller pieces.
- 2 2-pin female headers
- 1 custom PCB – $1.12
The total unit cost was $2.81, plus time and solder. I’ve decided to sell off the extras either as PCBs or as kits, so let me know if you’re interested by commenting below.
Here’s the schematic and a screenshot of the PCB design, as well as a larger version of the image above:
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- DIY 12-channel Bidirectional Logic Level Shifter / Logic Level Translator, using AMS1117, MOSFET pass transistor interface, and 2N7000 MOSFET transistors.
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- Schematic for 12-channel Bidirectional Logic Level Shifter
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- PCB for 12-channel Bidirectional Logic Level Shifter
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- Logic Level Shifter Hacked for Nokia 5110 LCD
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- Logic Level Translator with Nokia 5110 LCD
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- Logic Level Shifter with Nokia 5110 LCD Mounted
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- 12-Channel Logic Level Shifter/Translator PCB, Top
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- 12-Channel Logic Level Shifter/Translator PCB, Bottom
I used the excellent Quick KICAD Library Component Builder recently to build a new component for eeschema in KiCAD, but when I imported the library, I got an error dialog that said, “Library
KiCAD Eeschema Component Load Error message
It turns out the exception was caused by a space in a pin name: I had typed “SER IN” as the name of the pin, where I should have used an underscore and typed “SER_IN”. The library utility doesn’t prohibit this, and KiCAD clearly doesn’t like it.
Before I placed my order, I had questions about Seeed Studio Fusion PCB service turn-around time for shipping to the USA, and so I figure others might as well.
Here are details of my order of the ten 5cm square PCB’s shown in DMD: Dual Motor Doohickey (Modular RBBB and TB6612FNG Driver Board). The total cost was $13.42, including shipping (subtotal $9.90, plus $3.52 Registered Air Parcel). There were no “extras” (like 100% e-test, special colors or shipping methods, etc.).
- 8/02/2011
- 7:52 AM – Order placed. The total charge appeared on my PayPal account six minutes later, and the order confirmation with order number arrived at the same time.
- 8:47 AM – I added the order number to the silkscreen layer of the PCB as requested and sent the gerber files to the email address specified about an hour after the order was placed. The design and gerbers were created with Fritzing.
- 6:26 PM – Received an order update email: The order has been changed to status “Processing.”
- 8/03/2011, 4:37 AM – Received an order update email: The order has been changed to status “In production.”
- 8/04/2011, 1:49 AM – Received a person email from Dwin, I assume because when I ordered I had asked them to let me know if there were any problems: “Your PCB is under processing. If the file and design meets requirements, they will be processed and shipped in 4-6 working days.”
- 8/08/2011
- 4:33 AM – Received an order update email: The order has been changed to status “Traceable.”
- 4:56 AM – Received an order update email: The order has been changed to status “Shipped.” (Yay!)
- 9:21 PM – Received an order update email with a link for tracking the order.
- 8/09/2011, 4:44 PM – Tracking status: “Acceptance” at Hong Kong; Tracking status: “Origin Post is Preparing Shipment.”
- 8/11/2011, 10:53 AM – Tracking status: “Processed Through Sort Facility” at Hong Kong. “The item left Hong Kong for its destination.” (United States of America)
- 8/23/2011
- 7:29 AM – Tracking status: “Arrival at Unit” at my local post office.
- 4:01 PM – Delivered. I actually received 12 (instead of 10), and they all look great. They were very well packaged in a small corrugated cardboard box with lots of bubble wrap.
That’s 21 days or three calendar weeks start to finish — not bad at all! Tonight, I solder!
Math Monday came early this week, and we had some fun exploring Reuleaux triangles. Next to a circle, they’re the simplest curve of constant width you can make — that basically means you can roll a plank on top of them as smoothly as on wheels. The kids didn’t expect that one! (They also would make great manhole covers!)
Although they roll very smoothly, they do tend to wobble around a bit, so I built a little gutter on the plank to make it easier for the kids to experiment with. It was a quick project, and lots of fun for the kids. You don’t have to use a band saw or even the sander; all you really need is a jigsaw or coping saw, some scrap wood, and some nails.
Music credits: “260809 Funky Nurykabe” by spinningmerkaba (CC-BY 3.0)
http://ccmixter.org/files/jlbrock44/29186