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Adc for Gadgeteer is on the way


#1

I finally got some spare time to try to finish up my ADC board. I used MCP3424 chip from Microchip, which has the capbility to work at 18, 16, 14 and 12 bit resolution, software selactable and it has 4ch (differential). For a specific use I needed a R/R rail to rail opamp (MCP6284) with shottky protection diodes as signal conditioners. The Board uses 5V, but has a standard circuit with N-Channel mosfet to manage 3.3V to/from 5V for I2C (hardware) to gadgeteer boards. This board need to be used in a middle power RF field very close to HF antennas, so I needed a R/R clean front-end to avoid RFI on the input.
Becouse I need 6 analog ch I used 2 MCP3424 chip on this board. I provide also a passthrough gadgeteer connector so you can attach 2 of this board obtaining 16ch, and a configuring jumper.
This ADC converter is not very fast indeed and it can reach 260 SPS at 12bit, but only 3.75 SPS at 18bit.
The board routing is just rough and not optimized nor gadgeteer compiant for the moment.

[Edit:] I used differential input as single- ended.

I’m thinking if may be better to have a single chip (4ch) board instead of two chip (6ch), becouse it will cost much less.
Any suggestion ?


#2

looks very cool :slight_smile:


#3

Very cool!

First thing that comes to mind is that it doesn’t follow Gadgeteer Module specification in terms of socket labeling, orientation, mounting holes, Gadgeteer logo etc.


#4

As Architect mentioned, please make it “gadgeteer” please :slight_smile: Just open any of our designs and copy everything you need, rounded corners, holes, marking…etc.


#5

@ Gus - This is just a dimension evaluation board routing and as I wrote in the post is not ready yet. Will work on that next days.


#6

Excellent :slight_smile:


#7

Cool!

Agreed.

Does the current design require two “I” sockets from the mainboard or is the second one for chaining additional modules?


#8

Both are I sockets according to schematics.


#9

I see that but it’s not clear to me what his intent is. Since the nature if I2C allows chaining of the components w/o multiple sockets, he could get by with just a single socket. So, is the second one for chaining others or are the chips not chained under a single socket?


#10

As long as addresses are different which probably not the case with these chips.


#11

That’s what I’m suspecting also. If that’s the case, it makes more sense to me to have each chip on a separate module.


#12

The socket are intended to be “I” socket to be used for i2c chaining, but I made an oversight to connect some wire like GPIO int pin 3. This ADC chip have 2 addresses pins A0-A1 that can be used to choose 4 different address, making them suitable for chaining till 4 chip/16ch. So making 1 chip (4ch) board I can chain 4 board (total 16ch), and with a 2 chip board I can chain 2 board (same total 16ch).
This is to avoid the problem of using all the I socket of a mb if more channel (max 16ch) are needed.

I don’t remember if the “extension” connector need to call “*” or “I” … I will look in the gadgeteer specs sheet but it will be useful to chain i2c sockets.

As I state in my first post, 1 chip board costs little more than half a 2 chips board. So I’m thinking and asking suggestions on what the best solution.


#13

I don’t remember the specs discussing chaining anything other than DaisyLink. I don’t know that I follow that convention since it could add confusion. Maybe an “I Next” socket? Justin typically just uses a different cable type. At this point it seems that you can do whatever you want.


#14

At first look you are right, no info on this case. The two gadgeteer socket will be abolutely identical, so you can attach one or the other to mb without problems. The “I next” could be good idea. I will try a downgrade for the board to just 1 chip (4ch) making it 4 board chain possible … It will be smoller and cheaper.

I make my board at Eurocircuit, they work very well, but black silkscreen is an absurd expansive option for small batch … damned guys. :o)


#15

You may want to check out dfrobot.com. Only $3 to upgrade to black mask.


#16

@ ianlee74 - Thank you Ian, I checked it and really it costs much less than Eurocircuits. I will see for shipment, becouse it’s a problem getting goods from US due to real looong custom clearance and we have now VAT ad 21%.


#17

dfrobot is in China and with the DHL option it usually only takes about 3days to reach me in the U.S. 10 days from the start of production.


#18

Yes, I realize that soon after the post.


#19

@ dobova - introduce yourself to Lauren at dfrobot and say Justin and Ian sent you from tinyclr.
they are really good and quality is excellent and Lauren will look after you :slight_smile:


#20

@ Justin and Ian -
Oh waw, thank you guys !!!