Soft latching switch module

While working on some of the adaptive toys(Star master light) it became apparent that a latching switch would be a better fit for certain functions than the momentary ones currently in use.

In discussions with @MMC_Jake it seems the preferred approach is to have a separate device that interfaces with existing switches rather than a redesign of the switch to hold an off the shelf latching switch.

On the surface this seems to be a relatively easy build but I’m pretty new to MMC so am not aware of all the situations that the switch may be used in.

Certainly for toy adaptations, I think something like the attached would suffice

We could certainly use mosfets if necessary and fiddle with the RC values to ensure the switch doesn’t oscillate if held down too long.

There is another similar circuit from EEVblog that may be a little more thought out (in particular his final design doesn’t draw any power when the switch is off.). Comment section has a recommended change.

One factor to consider is the need to get Vs and ground to the latch. For most toys we could simply pull that from the mono cable or use something like the battery interrupter .

Appreciate any thoughts or input. I know just enough to be dangerous about electronics so would welcome any comments, including whether this is worth pursuing.

Marc

Integrating a latching/toggle function directly into a switch is certainly an option, but I think having an in-line device like this would be more broadly applicable for use with a range of switches. There are a couple of related projects, but I believe an inexpensive, standalone soft latch / toggle would be useful. Would be nice to get some insight from users.

There are couple of related projects:

  1. Switch Modifier (https://www.makersmakingchange.com/project/switch-modifier/)
    This device latches the output for a specific and adjustable hold duration. It is battery powered and uses an microcontroller, all housed in a 3d printed case. Hold time is set by adjusting a potentiometer. Cost of materials/shipping is ~$50. Designed by Rachelle Bernier at Stan Cassidy Centre for Rehabilitation.

  2. Tiny Switchy (https://www.tinyswitchy.com/)
    This device has both a toggle mode and a timed latch mode with adjustable time. The device is powered by a coin cell. It uses a microcontroller and a custom PCB mounted inside a custom plastic enclosure. The hold time is set by pressing and holding a push button for the desired time. Another push button is used to switch between the timed latch and toggle modes. Under development by Dale Grover (@dgrover).

I can certainly imagine this as maker-friendly build with a custom PCB and thru hole components. Another option for a cheaper/smaller device would be surface mount components (and possibly assembled along with the PCB), though that poses the cost/quantity distribution challenge.

From a design point of view, would need to consider the ability to handle sufficient current to operate some of the more power-hungry toys and power efficiency in the case of a battery powered device. Tapping into the toy’s power/ground using a (modified) battery interrupter is an idea worth exploring, though this approach may be limited by the number of toys where that is possible. @MMC_Derrick can probably weigh in on the circuit.

Thanks Jake, was trying to avoid microcontroller based in order to keep it simple, lower cost. They do provide some flexibility though.

Most toys will have access to the battery compartment so accessing power there wouldn’t pose a challenge in most cases. If we go that route (rather than pulling through the switch attachment) I think we should use barrel connectors to avoid reversing the connectors accidentally.

As far as the circuit goes we could look at options that reduce the number of components (555 timer base ones or purpose designed flip flops), slightly higher costs but easier to assemble ?

I’ll be playing with a couple of circuits I’ve found just to see if they work as advertised. Need someone with circuit analysis skills before deciding anything of course. Lots appear to be missing pull down resistors or default to on when powered etc.

Marc

1 Like

I think avoiding a microcontroller is definitely the right direction for this one.

Just had a conversation with some OTs and a Rehab engineer around how useful something like this would be for gaming - specifically the ability to use the shift functionality with the Xbox Adaptive Controller without having to press and hold a button down.

A battery powered solution would probably be the most broadly usable, even if that limited the amount of current it could switch.

Thanks, do you know which input is the shift functionality ? Or is it a combination ? Looks like some ports are analog and some are digital.

Within the Xbox Adaptive Controller profile setup, you can set one or more of the input ports to act as a shift button.

Xbox Adaptive Controller Shift button setup

You can then add a shift action to any of the different input ports so that one button can be used for two different actions.

XAC Button with Shift

The shift function can also be used to allow one stick / joystick to control both the left stick and the right stick, or vice versa.

A hardware toggle would be useful for users who aren’t able to hold the shift button down. (E.g. a user who is able to access 3 buttons with one finger could use one button as shift and gain an extra input)