Hmm, taking that into considerations, BNC may not be viable
The more I think of it, the more I like Cyrus’ idea that we incorporate relay latching LEDs. Shall we just go for the ATmega 2560? Or stick with the 644? It would be very helpful for planning if we can begin to nail down some component specifications.
Lets go with Atmega 2560, it will give us room for expansion in future, if we would go with Atmega644 and in future we had to add something that would need us to go back to the design or use more pins, we would have to design the whole thing again!!!, so i would prefer 2560
Wooh Atmega 2560 is an overkill dont you think
Gearbox, can we reliably handle 402-sized SMT components? e.g http://www.digikey.com/product-search/en?keywords=445-4890-1-ND.
What do we think about just using screw terminals for all sensors, as shown in the following image? Note the off board LCD and buttons. http://www.fujitsu.com/jp/Images/interface-board_tcm102-2657283.jpg
Oscar actually this is really cool I love it Plus we already have lots of them in stock at Gearbox
Good morning all. Sorry have been away for a while
Hi Oscar, we can have 4 terminals for the sensors (2- signal)(Gnd, 3V3/5V) The 3v3/5v terminal may be selectable by a selection jumper pins so we save on terminal block space
Finally Cyrus! you chose the 2560. I think your reason is very good. future expansion. we also have 256k programming space. I encountered programming space problems in splash board v1.0. I had to really optimize on the 32KB space to get things running. The micro-controller was very unstable when the space was approaching 100% full
Quick suggestion - now that we are going with the 2560 micro-controller, Can we upgrade the display system from 204 LCD to a more resolved display like the 12864. I am just thinking the sensor outputs may be better displayed here. You can also graph data. https://www.sparkfun.com/products/710
Great! MCU: ATmega2560. LCD:GDM12864H. ESP8266 for WiFi. 3 things nailed down :). Other considerations are:
- Are we planning to have a USB port? If yes, shall we use an FTDI chip, or the ATmega16U2?
- Can we increase the buttons to 6 (up, down, left, right, enter, exit) now that we have lots of IO pins?
- Are we using size 402 components where possible, or is it a minimum of 603?
- Are the LCD and buttons on a pluggable/unpluggable daughter board or fixed (elevated) to the main board?
- Can we agree on a two pin JST connector for the speaker? And adequately sized FRC connector for LCD or LCD and buttons?
- Again, with a multitude of pins available, lots of memory (and expansion in mind), shall we also include support for an SD card?
- Once all the IO is mapped out, we can make a final decision on IO ports based on the number we want from the available IO pins, and their physical aspects.
Lets constrain ourselves to 0603 components for now. Bob, Cyrus & others, what do you think of the other queries?
Here is a great tutorial on SMD devices >> http://www.topline.tv/SMT_Nomenclature.pdf
Here is a great link to SMD packages and their power capabilities >> https://www.google.com/search?q=smd+resistor+wattage&safe=active&client=ubuntu&hs=fIX&channel=fs&source=lnms&tbm=isch&sa=X&ved=0ahUKEwi2jfq-85XPAhUqJMAKHfo6A2EQ_AUICCgB&biw=870&bih=426#imgrc=MM2pHaUhhcq4OM%3A
size in mind, a sensitive selection criteria of SMD components, a trade off for size is the component power rating. We don’t want to burn things up
WRT 403, I was thinking of the MCU power decoupling capacitors and resistors (maybe ESD protection for IO pins), but 603 will be fine for it all. A nice link to resistor selection: http://www.ohmite.com/techdata/res_select.pdf. Other interesting docs on this topic: http://www.scienceprog.com/using-current-limiting-resistors-on-avr-io-pins/. With long wires to external circuits: http://www.digikey.com/en/articles/techzone/2012/apr/protecting-inputs-in-digital-electronicsl
I drew up a mockup to see what we could possibly do with the extra pins left after basing a design on: Atmega 2560 - 100 pin, ESP8266, SD Card reader and RTC with battery (SD fixture and Battery holder are not shown because they would fit on the reverse side), LCD and speaker headers, 6 long-stem tactile buttons, RGB LED and a few other components. Generally 603-sized components are ignored because they will always fit in.
Anyway, It seems we can fit it all in the 100mm x 150mm board, with all (approx 46) extra pins broken out to screw headers. All that this shows is that the size will work and that we can break out all pins if needed.
Thanks oscar. So we can minimize on board size, and optimize on design, i suggest
- We have programming slot we can plug FTDI for programming or debugging. (instead of having it on the board)
- Shifting the buttons and LEDS from the main board, and having them on a smaller daughter board that connects to the main board via ribbon cable and can easily stretch to the top face of the casing- giving better access to these parts from outside
- having the LCD connect also through a ribbon cable
- having a loud piezo buzzer in place of speaker
- we can add support for SD card reader
Hi Michael, and thanks for your comments. In the sketch above the LCD is connected by cable, so is the speaker (CEM-1203) which resembles a piezo element but allows a wide range of frequencies. This allows us to have different tones instead of having a single frequency buzz for everything.
Anyway, I will take your suggestions on board. Thanks again.
P.S. It’ll help me greatly if you could sketch out your layout concept graphically too.
Hi Oscar, I will sketch out and upload soon
Hello guys, almost done with my sketch will upload later
Thanks Cyrus. Let us do only the schematic first, then post here. Printed circuit board design will come much later once we complete the schematic and review the concepts here