electromagnetic switch question from a novice - Page 1
Forum section: electronics / general

author: quadfather
author_rank: Newbie
timestamp: December 25, 2013, 06:08:27 pm
content: I'm looking for a magnetic pick up switch that is adjustable. a switch that wont close until the pulses reach an adjustable speed threshold. is there such a switch? what is it called? where can I buy one? I apologize for my electronic ignorance.

author: Jeroen3
author_rank: Super Contributor
timestamp: December 25, 2013, 08:16:58 pm
content: A quick google shows that Eaton has inductive iProx sensors which are programmable. Sure others might have this too.They also sell analog sensors, which you can put in an differentiator module or whatever device you can find or build.Note that some of these inductive sensors have a low refresh rate because of their operating principle.

author: pyrohaz
author_rank: Regular Contributor
timestamp: December 26, 2013, 04:07:06 am
content: You could try:Reed switch -> Frequency to voltage converter -> ComparatorThat should give you a frequency controlled magnetic switch as long as you don't exceed the reed switch speed (sometimes up to 1kHz).

author: Rerouter
author_rank: Super Contributor
timestamp: December 26, 2013, 04:09:43 am
content: you didn't say what country your in, but in most cases you should be able to get away with a cheap inductive sensor and a rev switch module (automotive people want a light to come on when they enter they red line or the ideal gear change point, so these modules are fairly cheap)

author: quadfather
author_rank: Newbie
timestamp: December 26, 2013, 06:20:30 am
content: I'm from the u.s. I'm a supervisor of dump truck drivers. A problem that all dump truck drivers have is sooner or later they will leave a job with their dump bed still in the air. they can hit bridge overpasses and high powered lines, it can be serious and costly in lives and dollars. what I would like to do, if possible is take the signal that comes from the tone ring of the anti lock brake system and use it to have an alarm go off in the cab when these 2 conditions are met: the power take off is engaged, the truck is going 5mph or faster. we have a system now that is ran by a limit switch on the frame of the truck that operates a warning light in the cab any time the bed is raised; however, if the driver doesn't notice the light it does no good. we use a light in this system because the constant alarm would be very distracting to the driver. anyway that's why I was wondering if there was such a thing as a switch that could read the tone ring signals and close when the speed increased to more than 5mph that way we could utilize an audio alarm to alert the driver.

author: SeanB
author_rank: Super Contributor
timestamp: December 26, 2013, 07:03:12 am
content: I would not tamper with ABS sensors, as it is quite dangerous if you get something wrong, and it is a legal liability issue. Can you not use a switch to detect when the gearbox is selected out of neutral ( often an option on the gear selector switch on any auto box) and use that instead. Otherwise a tone ring and ABS sensor on the output shaft of the gearbox, or an engine speed sensor on the output shaft gearset to detect movement as a stand alone modification would be better.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 26, 2013, 10:16:14 am
content: as many others have adviced and i did that to my car (to disable starter engagement by accidental key turning during engine ON), tap the digital tachometer from ECU (or the analog with additional level shift circuitry). the digital tach is PWM proportion to engine speed, but in you case you should tap vehicle speed PWM IO line (you can tap the hall sensor directly but i dont thats a good idea) and then you can search F to V circuit feed to comparator. care must be taken not to load the tapped IO signal unnecessarily so it will screw other built-in circuit.

author: Rerouter
author_rank: Super Contributor
timestamp: December 26, 2013, 10:37:44 am
content: if you have any vdo resellers nearby you the part your after is a 660.990, we fit them to buses with a similar purpose to kill the door switch over 2.5kmph

author: Jeroen3
author_rank: Super Contributor
timestamp: December 26, 2013, 01:36:20 pm
content: If it is a quite modern dump truck there might be a software solution already in there.Otherwise, why don't you ask the manufacturer of the dump truck?If you want a diy solution, maybe you can tap a signal indicating the truck is set in gear.Or tap the switch system used to stop the hydraulics, there must be something in there.

author: Mechatrommer
author_rank: Super Contributor
timestamp: December 26, 2013, 02:22:13 pm
content: if the dump truck is pretty advanced, then it might have ee dump system you can tap, i never heard one maybe i'm not in the business. the hydraulic system (dumb, cement mixer, firefight pump etc) that i've seen are all mechanical gear shift like to activate hydraulic. yes it depends on what you have. but even the alarm system you have to "diy led" and the possibility of hitting something bad indicating it might not that advancedYMMV.

author: quadfather
author_rank: Newbie
timestamp: December 27, 2013, 01:33:45 pm
content: rerouter, do you guys tap the line on the abs or do you install another tone ring? thanks in advance.

author: ConKbot
author_rank: Super Contributor
timestamp: December 30, 2013, 09:22:29 pm
content: Definitely check out tapping into the J1708 or 1939 bus (industrial truck equivalents of OBDII and CAN bus) J1708 may have the gear selection and will definitely have speed and RPM, and maybe even a PTO status. If it has speed and PTO, then you can have your device just sniff the bus and make horrible noises when they are doing something naughty. If not, then sniff the bus for speed, and then monitor your existing indicator for if the bed is up.Running wiring etc for long term instrumentation on a vehicle that is going possibly off road is doable but takes careful consideration, and would increase the time to install each device by quite a bit. If you can just get a device which uses cheater taps to steal the signal from the 1708 bus leaving the diagnostic port free, and it can be out of the way where it may be disabled by an annoyed operator.