Wednesday, December 23, 2015
V1 boards are in!
Looks like OSHpark beat DirtyPCBs on delivery time this time around. Now let's see if the boards work at all... I'll start with the LED and UART test today.
Wednesday, December 9, 2015
PCBs have been submitted to the board houses!
Quick update -- I submitted my PCB to OSHpark a few days ago, and to DirtyPCBs yesterday. We'll see what the differences are, and how quickly each service turns the boards around!
I also ordered a ton of components from Digikey, so once I have everything in hand, you can be sure to see some status updates here.
Keeping my fingers crossed, hoping that I won't need to do a rev of the board!
I also ordered a ton of components from Digikey, so once I have everything in hand, you can be sure to see some status updates here.
Keeping my fingers crossed, hoping that I won't need to do a rev of the board!
Saturday, December 5, 2015
First pass at PCB is done!
I've been spending a few minutes here, a few minutes there, and am close to having something to send out to OSHpark. Here's what it looks like at the moment:
And here's what the BOM looks like right now:
| Description | Part Number | Unit Price | Discount Price qty 100 | Qty | Total | Discounted | URL |
| PICAXE-14M2 | $3.39 | $3.19 | 1 | $3.39 | $3.19 | http://www.robotshop.com/en/picaxe-14m2-microcontroller-chip.html | |
| USB-RS232 converter | CH340G | $0.40 | $0.40 | 1 | $0.40 | $0.40 | aliexpress |
| PCB | $1.00 | $1.00 | 1 | $1.00 | $1.00 | OSHpark | |
| green SMD LED | 160-1169-1-ND | $0.30 | $0.13 | 1 | $0.30 | $0.13 | http://www.digikey.com/product-search/en?keywords=160-1169-1-ND |
| 22pF capacitor, SMD | 399-8165-1-ND | $0.16 | $0.05 | 2 | $0.32 | $0.11 | http://www.digikey.com/product-detail/en/C1206C220K5GACTU/399-8165-1-ND/3471888 |
| 0.1uF capacitor, SMD | 399-1249-1-ND | $0.10 | $0.03 | 2 | $0.20 | $0.07 | http://www.digikey.com/product-search/en?keywords=399-1249-1-ND |
| 12MHz crystal, SMD | CTX888CT-ND | $0.38 | $0.26 | 1 | $0.38 | $0.26 | http://www.digikey.com/product-search/en?keywords=CTX888CT-ND |
| 22k resistor, SMD | P22KACT-ND | $0.10 | $0.01 | 1 | $0.10 | $0.01 | http://www.digikey.com/product-search/en?keywords=P22KACT-ND |
| 10k resistor, SMD | P10KACT-ND | $0.10 | $0.01 | 1 | $0.10 | $0.01 | http://www.digikey.com/product-detail/en/ERJ-6GEYJ103V/P10KACT-ND/43118 |
| 200ohm resistor, SMD | P200ECT-ND | $0.10 | $0.02 | 1 | $0.10 | $0.02 | http://www.digikey.com/product-search/en?keywords=P200ECT-ND |
| TOTAL | $6.29 | $5.19 |
I'm going to get pretty close to the $5 cost target! After I do a quick review, I'm going to get this thing made and see how hard it is to assemble. Hopefully, it works. :)
Wednesday, December 2, 2015
Identifying a really cheap embedded solution that is ideal for schools
As I said in my previous post, a few dads and I are going to help out with a Maker's elective at school. The three topics we will be covering include plumbing, woodworking, and electronics. Of the three, I'm probably most skilled in electronics, so that's what I am going to attempt to "teach".
My goal is not going to be to make the kids experts in electronics. Heck, I'm not an expert and just kind of hack my way through projects. I just want them to be comfortable enough with the basics that they will be able to work on their own projects after the course is over. In addition, I would like them to have fun and excite their curiosity so that they will WANT to pursue projects.
The basics include an explanation of voltage and current, Ohm's law, and Kirchoff's Laws. I will need to come up with analogies to make the concepts easier to understand, as well as piece together simple demonstrations to show how the laws apply. I would also like to give an overview of basic components, like resistors, capacitors, diodes, potentiometers, switches, and LEDs.
Blinking an LED when you press a button is nice for a "hello world" kind of electronics project, but to really capture their interest, I'm thinking that demonstrating fun things is the right way to go. For example, I might be able to hack together demos like the following:
I created a matrix of products that had to be cheaper than $20, but the magic price I wanted to hit was $5. That's a tall order, but I think I have reached a decision...
This matrix aims to evaluate each available platform in terms of cost, ease of use, my ability to help the kids out with them, as well as accessibility to programming tools and development environments.
I have decided to go with a custom solution, and am currently designing a simple PICAXE-based PCB that includes everything a kid would need on a stick that plugs into a USB board. It wouldn't need a voltage regulator because I would just rely on the 5V, 500mA USB port present on all computers. The USB-RS232 converter and PICAXE are both 5V compatible. I am currently going to go with the 14M2, which I believe will give them a reasonable amount of I/O to play with. The PCB will include all required components, as well as female stackable headers so that the board can be plugged into a standard breadboard for prototyping.
The other nice thing here (if it works!) is that this gives the kids an opportunity to learn soldering and assemble a mixture of through-hole and surface mount components. I am going to go with the largest surface mount packages available for each component so that it's easier for them.
If this works out, this board could be a really useful platform for future classes at our school, or at our engineering fairs. I'll open source everything so other schools can use it as well, not that there's really anything I'm doing here except assembling the BOM and designing a PCB...
If you have any suggestions about useful electronics topics for kids, or anything else at all, please post them!
My goal is not going to be to make the kids experts in electronics. Heck, I'm not an expert and just kind of hack my way through projects. I just want them to be comfortable enough with the basics that they will be able to work on their own projects after the course is over. In addition, I would like them to have fun and excite their curiosity so that they will WANT to pursue projects.
The basics include an explanation of voltage and current, Ohm's law, and Kirchoff's Laws. I will need to come up with analogies to make the concepts easier to understand, as well as piece together simple demonstrations to show how the laws apply. I would also like to give an overview of basic components, like resistors, capacitors, diodes, potentiometers, switches, and LEDs.
Blinking an LED when you press a button is nice for a "hello world" kind of electronics project, but to really capture their interest, I'm thinking that demonstrating fun things is the right way to go. For example, I might be able to hack together demos like the following:
- wiimote with accelerometer
- spinning a stepper motor to drive a car
- rotating a servo to move a Nerf cannon
- lighting up LEDs in series to emulate a Force FX light saber
- sound recording / playing (maybe to add to above light saber demo)
I created a matrix of products that had to be cheaper than $20, but the magic price I wanted to hit was $5. That's a tall order, but I think I have reached a decision...
| Dev Board | Cost | Extra Costs / Time | Solderable? | Free Programming S/W | Free Dev Env | Windows? | OSX? | iOS? | Experience? | Comments | Sources |
| MSP430 Launchpad | $10 | No | N | Y | Y | Y | Y | N | Some | Bringup takes time | TI |
| EZ430 | $10/$24 | No | N | Y | Y | Y | Y | N | Some | Not sure if alibaba pricing is legit | Alibaba.com |
| Cypress PSoC | $4 | Headers | N | Y | Y | Y | N | N | No | Cyproess | |
| Freescale FRDM-KL25Z | $15 | Headers | N | Y | Y | Y | Y | N | Yes | Bringup takes time, but really powerful tools | Digikey |
| Arduino variants | $15-20 | USB cable | N | Y | Y | Y | Y | N | Some | I don't like Arduino | Adafruit, Sparkfun |
| PICaxe custom | $3 | PCB, Headers, USB-RS232 | Y | Y | Y | Y | Y | Y | No | Coding is easy | Sparkfun, Aliexpress |
| PIC custom | ? | PCB, Headers, USB-RS232 | Y | ? | Y | Y | Y | N | Some | Not sure about cheap programming options | Digikey, Aliexpress |
| C.H.I.P. | $8 | Linux | N | Y | Y | N | N | N | No | Delivery date? We are also not teaching them about programming computers | getchip.com |
| Raspberry Pi Zero | $5 | Linux | N | Y | Y | N | N | N | Little | Impossible to get at the moment. We aren't interested in teaching Linux here | Element14 |
| Onion Omega | $19 | Mini dock | N | Y | Y | Y | Y | N | No | I have one, and the available libraries are quite limited right now | onion.io |
This matrix aims to evaluate each available platform in terms of cost, ease of use, my ability to help the kids out with them, as well as accessibility to programming tools and development environments.
I have decided to go with a custom solution, and am currently designing a simple PICAXE-based PCB that includes everything a kid would need on a stick that plugs into a USB board. It wouldn't need a voltage regulator because I would just rely on the 5V, 500mA USB port present on all computers. The USB-RS232 converter and PICAXE are both 5V compatible. I am currently going to go with the 14M2, which I believe will give them a reasonable amount of I/O to play with. The PCB will include all required components, as well as female stackable headers so that the board can be plugged into a standard breadboard for prototyping.
The other nice thing here (if it works!) is that this gives the kids an opportunity to learn soldering and assemble a mixture of through-hole and surface mount components. I am going to go with the largest surface mount packages available for each component so that it's easier for them.
If this works out, this board could be a really useful platform for future classes at our school, or at our engineering fairs. I'll open source everything so other schools can use it as well, not that there's really anything I'm doing here except assembling the BOM and designing a PCB...
If you have any suggestions about useful electronics topics for kids, or anything else at all, please post them!
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