Very Small Ammeter, connected to bluetooth.  - Page 1
Forum section: electronics / beginners

author: John-Thrust
author_rank: Newbie
timestamp: September 30, 2015, 01:40:30 am
content: Hi guys.I'm developing a device for a competition. The device involves a chemical which changes in resistence over time, but you don't need to worry about this. My design requires something very small in a circuit that can measure change in current over time, relay this information to a bluetooth transmitter, and have that bluetooth relay that information to a phone. In theory this should be relatively simple- I find a small ammeter, but it on the circuit, and connect that to a bluetooth device.I need to stress how small this device should be. We're talking the size of a fitbit or a watch, all things included.Reality, as often in life, has proven much more difficult. For the life of me I can not locate a small ammeter that I can just put on a circuit- everything I'm finding is big, bulky, and often includes a gauge which I don't really need.I also need help locating a small bluetooth device, an explanation of how it works, and how I would connect to anything I end up using.Conversely, is it possible to skip the ammeter altogether and just have the bluetooth part relay how much current it's receiving directly to the phone?Thanks in advance- any response would be really helpful.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 30, 2015, 02:49:10 am
content: How much current? For that matter, WHY are you measuring current?There are easier ways to measure conductivity/resistance across a couple of nodes.You don't need "an ammeter". The microcontroller IS the "ammeter".Depending on the impedance and precision needed, and the power available,it could be as simple as a resistor and an analog input into the microcontroller.It seems quite possible that the power source (3V "coin cell"?) would be the limiting size factor.Depending on what kind of programming resources you have, you could use something like the ESP8266 which is tiny, dirt-cheap and quite possibly a one-chip solution for both measurement and wireless communication in the same package.

author: John-Thrust
author_rank: Newbie
timestamp: September 30, 2015, 03:07:09 am
content: Quote from: Richard Crowley on September 30, 2015, 02:49:10 amHi Richard. The odds are, the current is going to be relatively small (10-100 mA). The basic idea behind measuring the current is that as a chemical which we are testing for reacts with a solid acid, more current is allowed to pass through the solid acid.I think I understand what you say about my "not needing an ammeter".I have very little electrical experience. Could I connect the wire running from the solid acid (you can think of it as a fluctuating resistor, where in the resistance changes over time) directly to the ESP8266? I can figure out how to program it, but advice would be appreciated. also, is the fact that this is WiFi conflict with bluetooth, or benefit it?Thanks so much sir. I a new comer in this field, but it's great to be getting help.

author: Richard Crowley
author_rank: Super Contributor
timestamp: September 30, 2015, 03:33:12 am
content: 10-100 mA is actually rather a large current for a small, battery-powered gadget.At what voltage? We still don't have any sense of the resistance involved here?What kind of power source is available? Voltage? Current? Size?Bluetooth operates on 2.4GHz just like WiFi. So operating the ESP8266 on Bluetooth is the matter of software. I don't know if there is a Bluetooth stack (software driver) for ESP8266. Or, for that matter why you need Bluetooth rather than the more conventional WiFi (IoT).You are asking architecture/design questions without revealing all the limiting factors of the project.

author: Connoiseur
author_rank: Regular Contributor
timestamp: September 30, 2015, 04:47:25 am
content: Quote from: Richard Crowley on September 30, 2015, 03:33:12 amRightly said. Your design will depend upon the resistance characteristic (linear/non linear). It might be possible that that you need to apply certain threshold voltage before you can be able to measure the current (and hence determine the resistance). Without these parameters specified, it's not possible to suggest a suitable design.

author: Cliff Matthews
author_rank: Unknown
timestamp: September 30, 2015, 02:53:35 pm
content: Have you played with a beginner level Arduino before? You'd have 10-bits of resolution to measure current with and the size requirement sounds like a $2 AVR nano could partner with a $4 bluetooth serial modulehttp://www.ebay.com/bhp/arduino-module-bluetooth. This could be powered by cheap 3.3v lithium coin cells.. and if you have to provide current for the chemical specimen, up that to a 3.6v flat L-ion cell.