Continue to Site

Welcome to our site!

Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

  • Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

confusing switch data sheet

Status
Not open for further replies.

MrDEB

Well-Known Member
am building a project that controls a truck radio that allows the driver to have the radio on for a selected amount of time in 5 miniute increments (uses a 7555, that uses 8.2M/33uf tantalum cap for timing) .The rancher wants to run his radio while feeding his cattle.
problem is I ran acreoo a lighted switch that has a confusing data sheet.(see pic)https://www.electro-tech-online.com/custompdfs/2009/02/MS-101102.pdf
the sheet shows 3 terminals but the data sheet also shows the switch has 4 pins (the 4th pin for the led)
another quandry I am having to decide is a 5v relay or a 12v relay.
the circuit can run on 12v but an automotive electrical system varies from 12 - 14 v.
If I go with a regulator then we may have a heat problem?? but the circuit will draw very little current.
the contacts on the relay, to be safe, are rated at 5A
any thoughts
 

Attachments

  • Capture2-26-2009-8.15.35 AM.jpg
    Capture2-26-2009-8.15.35 AM.jpg
    156.8 KB · Views: 138
The leakage current of a tantalum cap could cause timing variations with an 8.2M resistor. It would be better to operate the 7555 as a higher frequency pulse generator, which allows the use of a smaller resistor, and run the pulses into a counter, such as a 4060, to get the longer times.

The switch data is indeed confusing. It looks like there should be two terminals for the LED and two for the switch contacts.

The automobile electrical system can have large voltage spikes and transients due to such things as starter operation, so you should decouple the power to your circuit with a small series resistor and a large capacitor to ground, with perhaps a 15V zener to ground also. Otherwise you should be able to use a 12V relay. Relays are very tolerant of voltage variations.
 
the tantalum caps etc

the circuit explaniation states that the tantalum cap should be used for its lower leakage as well as using the 7555 instead of a 555
I first thought of using a divide by X counter then ran across the posted circuit link.
contemplating using a voltage regulator just to keep the timing circuit somewhat normal
either run with the caps/zenier diode as you suggested or a 7812 or 7805 regulator circuit.
not sure which??
yes the data sheet is confusing to say the least.
I couldn't get over the data sheets for the relays= no pin spacings except the the ones I have been looking at
still wonder if the 5amp contacts is overkill to turn on a car radio??
 
power supply questionable??

here is the schematic I have conjured up.
wonder about power supply overheating being its a 9v 78L09 with 12+ input voltage.
the transistor I think should be saturated with currents caculated using TINA etc.
any comments are welcomed
the orginal circuit states that using the cmos version of the 555 the rc network and 8.2M resistors should work (tantalum low leakage cap for C1)
as the previous post the data sheet is ????
 

Attachments

  • Capture2-28-2009-4.43.46 PM.jpg
    Capture2-28-2009-4.43.46 PM.jpg
    148 KB · Views: 108
I've used the 555 for several vehicle circuits without a regulator and never had a problem.
As for the relay contact rating, look at the radio fuse to see what it's rated at to give you a quick idea of current consumtion (or you could just meter it).
 
not my vehicle

but the contacts are rated at 10amps
should be enought for today's autos??
I need to check wiyth the rancher to see if I can measure the current draw etc.
the reason I put the regulator in the circuit is to keep everything on the same page and to prevent voltage spikes etc.
its just good pratice but worry about heat?? from regulator.
the 78Lxx series is a TO-92 case rated at only 100ma. not the 1amp of the 7809 which is in a TO-220 case
 
To answer the part about the 78L09 (TO-92 package), yes, it will work. If I see your schematic correctly, you are using about 60 mA of total current from the 78L09 for a power dissipation of (14-9)V×.06A=0.3 Watt. 0.3 W is within the free air dissipation rating for ambient temps up to 70 deg C. 60 mA is also fairly well below the 100 mA operating maximum, but not much margin for mods/expansion.
 
the schematic is the only load

the relay draws about 60ma but not much else.
my concern was regulaTING THE 12-14V PUT OUT BY THE TRUCK ELECTRICAL SYSTEM THEN DROPING IT TO 9V. WAS PLANNING ON GOING TO 5 BUT THEN ALL THAT EXTRA VOLTAGE HAS TO GO SOMEWHERE?? OUPS hit the caps lock--sorry typing with the religious method-seek and you shall find
voltage pikes shouldn't be a problem I hope.
relay is rated at 10amp contacts enought?? for a radio??
I need to check with the rancher.
 
To get some idea, 10 amps at 12 volts is a 120W radio. That be the case, that's a rock'in rancher with some hefty speakers to match. :)
 
he plays the radio for them cows-lol

I need to check with him on the radio size but the 10 amp relay is more than likely overkill.
never figured the watts but yea 120w is pretty good sized radio
coarse them cows demand the vibes---LOL
 
Status
Not open for further replies.

Latest threads

New Articles From Microcontroller Tips

Back
Top