555 Two-fer – Baby swing upgrade and a Headphone tube amp
posted Feb 24th 2011 4:01pm by Mike Nathanfiled under: home hacks, musical hacks
[Jason] sent in two 555 timer driven items that were worth sharing, both of which are entries in the 555 Design Contest.
The first item is a circuit that automatically resets an infant swing. [Jay], who built both items, has an infant swing for his daughter that spins a mobile and plays music. It’s great but it only works for 7 minutes and 15 seconds before a button push is required to trigger it again. He found this limitation to be annoying, and as I have owned the same swing, I can echo his frustrations. He probed the swing and found that a 5v pulse was required to reactivate the mobile, but it had to be sent after it turned off to have any effect. He put together a simple circuit that would do the button pushing for him, as you can see in the video below.
[Jay's] other entry is a headphone tube amp using a quartet of 6DJ8 vacuum tubes. The 555 timer in the amp is used to drive a FET and the hand-wound transformer he built for the amp. You can see a video of the amp in action below as well.
The projects are lacking a thorough write-up, but he does provide schematics for both the swing reset switch and the tube amp for those looking to replicate either item.
OK, the second one is kinda cool, but i’ve done the swing hack using nothing more than a switch, a capacitor, and a normally closed relay.
Connect a capacitor on the motor line to provide a constant signal when the motor is running. Connect this to the switching leg of the relay. Add a few diodes at the cap if the motor on yours is impelling both ways.
This way whenever the motor is running, the relay is open, and as soon as the motor cuts off the capacitor discharges completely and the relay snaps closed.
Add your switch just before the switching arm of the relay, and the whole thing will operate unattended for as long as you like.