| T O P I C R E V I E W |
| markbuts3 |
Posted - Jun 02 2004 : 12:56:08 PM
I have some motorised folding mirrors, and am wanting to get them to fold/unfold with the central locking...
So I basically need a circuit to take the short pulse from the alarm (lock/unlock signal) and convert it to a longer pulse (approx 2 seconds) which will energise a relay which will then provide power to the mirrors...
I am thinking I will have to use 2 of these circuits, one to lock and one to unlock..as the mirrors need different polarity to fold/unfold..
-ve earth btw...
I am a total newbie to circuits so please be gentle...
Thanks....Mark...
|
| 9 L A T E S T R E P L I E S (Newest First) |
| n/a |
Posted - Jun 25 2004 : 8:36:56 PM
200mA is the spec for the outputs from my car alarm, and I've got many relays connected to the alarm system. :)
However, it wouldn't help to have some protection for that IC to ensure that it does not become damaged. Automotive power systems are notoriously bad. The alternator doesn't respond very quickly to load dumps, and you can get some nasty voltage spikes. A 15V zener diode and a couple of reasonable sized caps are a good idea on the supply lines.
|
| markbuts3 |
Posted - Jun 25 2004 : 8:23:54 PM
Thanks for your help so far guys, I have drawn a circuit...http://mysite.wanadoo-members.co.uk/markb3/pics/finalcircuit.jpg
Does this look OK ??
Do I need the transistor switches, or can I just use pin 3 output to power the relay ?? (std 555 will source 200ma, is this enough for a automotive relay ??)
If I need the transistor switch, what transistor, resitor and diodes do I need ??
Thanks again.....Mark...
Edited by - markbuts3 on Jun 25 2004 8:29:21 PM |
| markbuts3 |
Posted - Jun 05 2004 : 5:27:56 PM
Thanks SupraGuy, I think I'll take your advice, once I get them (should be shipping in the next few days)..I'll wire them up with the std switch and time them, and also confirm the outcome of a longer pulse....
If it's as I've been told, I'll calc cap and resistor values for well in excess and leave it at that....
|
| n/a |
Posted - Jun 05 2004 : 02:25:44 AM
Why risk a mechanical failure of a pot? Just make sure that the circuit stays active for double the required time (or so) and leave it. If the motor circuit shuts off by itself, then let it do its job. Pots are great for a while, but an automotive environment is harsh on moving things. Why not just leave the pot out of the equation?
|
| markbuts3 |
Posted - Jun 05 2004 : 01:15:20 AM
Thanks for the ideas, the timing isn't critical, I have been told if power is applied for too long to the mirrors they will still stop at the closed/open position without the motor continuing, so I was thinking of a 3.3uf cap and 500k resistor with 500k pot, this should enable me to tweak the pulse length to plenty long enough....and make sure it is longer than actually needed...
This way, even with variation, the pulse should still be long enough....
Thoughts ??
|
| YS |
Posted - Jun 04 2004 : 10:38:36 PM
While your approach will work, it may be hard to adjust timing properly. Also, delay will depend on temperature. And your mechanism may change with temp. or time.
So, why not think of the following: alarm sets the trigger, which powers the mechanism. When the mirror reaches end point, the sensor (optical, magnetic with reed contact or just mechanical switch) resets the trigger and the thing stops at exact location.
|
| markbuts3 |
Posted - Jun 03 2004 : 8:51:09 PM
Thanks for your input Aaron... :)
|
| Aaron Cake |
Posted - Jun 03 2004 : 08:51:04 AM
Should work fine if you replace the trigger button with a relay.
As far as your component values, I don't know.  I rarely work with the 555 timer. They seem reasonable compared to other 555 circuits I have seen. Though you probably want to use a trim pot in place of a regular resistor so you have some adjustment.
|
| markbuts3 |
Posted - Jun 02 2004 : 1:51:07 PM
I found this......
Would this work if I replaced the switch with a relay (actuated by the trigger) ??
Using a calc program I found, I worked out values of R1..820 kohms and C..2.2 uF.....am I correct in these values for a 2 second output ??
|
