Splashboard V 2.0 IoT


Hey guys, sorry been away for a while will try to catch up. Great progress i see, :+1:



Hi guys, so here is a compiled circuit borrowing heavily on the concepts agreed and discussed above. Please review it.

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In the Upcoming meetup on 15TH, we’ll need to breadboarding and test some blocks concepts above:-

  1. The Instrumentation amplifier + digital potentiometer (for automatic gain to weak signals from sensor at Port A. - Ph probe produced very low voltage signal when dipped in acid. Splashboard 1.0 could not pick the values)
  2. Test the RTC circuit concept on a breadboard
  3. Test the Display block (128*64) graphical LCD
  4. Test the WIFI module
  5. build and test the switch mode voltage regulator circuit on breadboard

All these are separate modular tests.
we shall be using arduino mega(With 2560) to do these tests(keeping the schematic pinouts). Then if all pass. we shall move to PCB fabrication later on (as will be agreed )

what do you guys think?

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Ill need some help:-

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Cyrus, can you please help me create a short BOM for the Through Hole components we can source for testing on a breadboard?

here is some local stores:-

  1. http://store.nerokas.co.ke
  2. http://warefab.com
  3. http://ktechnics.com

BOM is simple, have it in this format

You can add LINK COLUMN after the last column where you will paste Links to the product so we can easily follow and find it. Thanks

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Oscar, can you please help me create an SMD component BOM list for the final pcb board? i know we’ll need to import the components. One of the great suppliers for the electronic components is Digikey. we also have Mouser among many others. Have all of them in a simple list, but with Links we can follow to view the product. it does not matter from where as long as its a component supplier, Will it be possible?

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If there is any change anyone may want to suggest concerning the schematic i’ve uploaded above, please feel free, it may not be the final

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Great work Michael!

I’m happy to look up components for the SMD BOM.

My questions/comments regarding the schematics are as follows:

  1. Power supply

a. According to the datasheet for the LM2576 in pg. 15 at http://www.ti.com/lit/ds/symlink/lm2576.pdf - “To maintain stability, the regulator input pin must be bypassed with at least a 100-μF electrolytic capacitor.” Are we skipping this by design?
b. The schematic shows the LM1117-3.3 connected to 12V. As discussed earlier, this would generate substantial avoidable energy loss. By coupling it to the LM2576 output, we would reduce this as well as be able to replace S1 with a single –pole switch. What do you think?
c. Is C9 used as an additional output capacitor, or is it part of managing output voltage ripple? If the latter, we probably need to add an inductor to complete the LC ripple filter.
d. Similarly for the LM1117-3.3, http://www.ti.com/lit/ds/symlink/lm1117.pdf, pg 14 recommends an input capacitor.

  1. Menu buttons

Because we have many free pins, should we not just connect them directly without using the resistor ladders? Given that there might be a wide range of temperature experienced in the casing (see 1b above) , going directly to the MC pins might improve reliability.

  1. Digital pot – MCP4131

a. The schematic shows the wiper pin P0W connected to P0B (notations changed to match datasheet). Does this work?
b. Because we have multiple devices on the SPI bus, and will also use it for ISP programming, I believe we should have 4k7 resistors in line between the ISP header and the other devices. What do you think?

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Ok Michael on will get to it immediately



Hey @Michael, here is the BOM for the splashboard.Can be edited on Google docs

I haven’t found the following part in the local stores MCP4131 but will continue searching for it or its equivalent.
Also please confirm if there is something i have missed.



Hi cyrus, Great work there! here is an equivalent digital potentiometer >> http://store.nerokas.co.ke/index.php?route=product/product&product_id=648



Cool will add it to the list



Updated Bill Of Materials

Note: I haven’t included Atmega2560 on the BOM



Hi Oscar, Thanks for the review. Those recommendations are very good:-

a) The Regulator is designed to handle unregulated
DC voltages. I suppose that the power supply we shall use is a stable
12V DC adapter with some LPF at its output stage (to keep the voltage
stable, regulated at 12V). I suppose it is very wise to still add the
100uF for robustness. I shall add

b) Correction is noted. Good suggestion. I’ll shift the regulator to the output
c) C9 is used to maintain output voltage. LC filter is optional. The
ripple is very small. may not be significant in most applications. we
shall however test this concept on a breadboard and use oscilloscope at
Gearbox to verify.
d) Noted. an input capacitor shall be added

2) Menu buttons shall not be on the main board(for
easy external acess to the top face of the casing). since we shall be
having a daughter board with LEDs and the Menu buttons, i was thinking
we could minimise the number of wires connecting the two boards(from 6
wires to 2 wires for buttons).
the circuit resistors can be tuned to
have atleast 1volt margin between the close states of the switches.
currently the minimum margin is 800mV, which is still not bad. It must
be a very noisy(EMI) environment to generate such on a network with such
an impedance and length. We can also test the concept this weekend on a
breadboard using ardino mega. before PCB fabrication

3) I have connected the 3 pin potentiometer as a
rheostat (2 pin) by connecting the wiper PW0 to one of the two ends of
the potentiometer P0B. It will work. we shall also breadboard to test
the concept and be satisfied before PCB fabrication

b) Noted. The SPI Lines shall be pulled High by 4K7 resistors



Hi guys. I like the enthusiasm you have and I must say I’m learning alot. Would you consider using this tft screen (http://store.nerokas.co.ke/index.php?route=product/product&product_id=803&search=lcd) instead of the lcd since it comes with sd support inbuilt a the same cost.



Chege: Welcome!, good to have you join us. The TFT screen is great and we would probably use it in future - I think the specs are now locked down as we design our schematics. But I could be wrong.

Michael: Could we please have the specifications for the interface of the pH meter and color sensor? It’s difficult to check the opamp configuration without knowing what input ranges to expect.

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Hi chege. Welcome aboard! we are happy to hear your comments. The TFT screen as Oscar said we may have it considered in the future if we shall decide to make a third version of the spashboard, owing to the advancements done on the second version

Here is the data to the pH probe.



please note that the PH probe has a signal conditioning circuit board that takes in the raw signal from the pH probe {ranging -414.12mV to +414.12mV}, amplifies and spreads the value to a range of 0(very acidic)-5volts(very alkaline), The problem we had with splashboard 1.0 is that the ATMEGA328 chip could not read the small voltages in the order of mV generated from the system when the probe was dipped in an the etchant of a very low pH. the ADC hardware within the uC would not resolve the fine voltage from the signal conditioning circuit board and so the value was always 0 out of 1023 (10 BIT ACD).

amplifying the signal and compensating the gain in the code for the probe measuring acidic fluids thus seemed to be the better solution.
what do you think?



Here is the updated schematics:-



Its okay cyrus, we can use arduino mega to do the testing



Hi Michael, thanks for redoing the schematic. There is still a thing to check though:

  • A bit important, the SPI termination resistors are supposed to be in-line, and not pull-up. Putting them AFTER the programming ISP header connection allows the ISP programmer to take precedence over other ISP peripherals (AVR - ISP connector - resistor - other SPI devices).

Looking forward to Sat.