Cheap load sensor - Page 1
Forum section: electronics / projects

author: lion
author_rank: Contributor
timestamp: September 09, 2016, 09:02:47 am
content: Hello EEVBlog community,I'm building a load sensor project where I have a lamp that is switched to another when it fails. For that I'm using a CSLW6B40M + PIC + Relay to activate the backstage lamp when there is no load.However, I find CSLW6B40M expensive. Do you know any replacement for this component or an equivalent sensor (up to 40mA Sensor).

author: Chalcogenide
author_rank: Regular Contributor
timestamp: September 09, 2016, 09:32:44 am
content: What about using a integrated hall effect current sensor, such as an allegro ACS712?

author: Kleinstein
author_rank: Super Contributor
timestamp: September 09, 2016, 10:00:33 am
content: Sensors for AC current are often much cheaper, as they can use a current transformer instead of hall effect.There might be the option to use a LED light instead of classic incandescent. So failure is much less likely.

author: lion
author_rank: Contributor
timestamp: September 09, 2016, 10:48:05 am
content: Quote from: Chalcogenide on September 09, 2016, 09:32:44 amThanks for the response. Do you know any made circuit that is applied to what I want?Quote from: Kleinstein on September 09, 2016, 10:00:33 amI'm using LED. Do you know any AC current sensor that I can use for 11W maximum ?

author: Alex Nikitin
author_rank: Super Contributor
timestamp: September 09, 2016, 11:57:36 am
content: Perhaps you can use a simple NC solid state relay (i.e. G3VM-353G from OMRON) - the relay LED with a diode bridge (and a small smoothing capacitor) in series with the first lamp and the second lamp operated by that relay. A fuse in series would be in order too. While the first lamp is drawing current (anything from 3 to 50mA), the second lamp is OFF. A little more elaborate circuit would give you a well defined current ON/OFF points and some hysteresis, so there is no chance that the relay would end up in a "half-open" condition and over-dissipate.CheersAlex

author: JacquesBBB
author_rank: Frequent Contributor
timestamp: September 09, 2016, 12:25:17 pm
content: Quote from: lion on September 09, 2016, 10:48:05 amMaybe you can look to my threadhttps://www.eevblog.com/forum/projects/acs712-and-esp8266/This very similar to what I want to do, although will higher current, but it could be very similar.

author: Kleinstein
author_rank: Super Contributor
timestamp: September 09, 2016, 12:57:36 pm
content: For AC current one could use just a ring core inductor as a current transformer. May not be very accurate, but is just standard parts (Inductor, resistor and diodes to protect against to much current. AC to detection can be done by the µC. One finds this in some vacuum cleaners with automatic start from load, so about the opposite of what you want.

author: DaJMasta
author_rank: Super Contributor
timestamp: September 09, 2016, 05:19:03 pm
content: Yeah, if you don't need accuracy or calibration, just on or off, then it should be a fairly simple thing to do. You can go with a straight current transformer for a known output (and still pretty cheap), but you can literally take some regular wire, wrap it around your mains line for a few turns, send that through an opamp with a good bit of gain, then send it throw a peak and hold circuit (more op amps) or rectify it and put it into a cap or something and just sample from there. As a proof of concept, I took a 6" breadboard lead, wrapped it three turns around my tablet's charging cable (AC side of the brick) and hooked it up to my scope... about 10mV peak to peak over a noise floor around 5mV - more than enough to get usable on/off data and this is with a loose winding outside of the insulation of the main cable.The relay seems like a pretty solid plan too, so you have options.