Keypad Emulator via hm-10 from IOS/Android app

I am attempting to make a touchless keypad connection for a keypad. Pre-Covid people would walk up and use keypad (3x4 numeric) to select products to dispense. I would like to add a Bluetooth receiver (HM-10 connected to an Uno is what I have) that would take the ascii command from the Bluetooth app and relay it through the same harness as the physical keypad. Essentially replicating the keypad button press to another controller in the machine. I am thinking a y harness to add Uno and BLE.

I am a novice but have successfully wired the keypad to the uno and can see the keypad button presses via the serial monitor using the keypad.h library. I have also successfully wired the HM-10 to to Uno and am able to see ASCII commands sent via IOS BLE terminal app. I am struggling with how to send the Bluetooth data back through the 7 pin keypad serial connection.

I would be grateful for any assistance.

It’s not that simple…

To drive an external “host” matrix keypad either need a load of transistors to try and “simulate” the actual physical button connections. Probably you can get away with 7 transistors, all connecting to a common bus if you only want to press one button at once and are sharing ground with the “host” device.

There’s some discussion here about how to do it and remain electrically isolated from the other device.

Or you need to read the input rows of the keyboard matrix (as being driven by the host when scanning the keyboard) react to them, and the connect the appropriate column to ground while keeping all the other pins as inputs (assuming a inverse “Short to ground” keyboard logic). This requires you to respond very quickly to the incoming row changes, otherwise you the external device will misinterpret key presses as being in the wrong row.

Thanks for the direction! I was hoping it would be that simple!