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Forum Index : Microcontroller and PC projects : PicoMite VGA - USB to PS2 Keyboard Adapter
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| Bleep Guru  Joined: 09/01/2022 Location: United KingdomPosts: 509 |
Hi Leo, Your easiest first option is to try powering the keyboard with 3.3V some will work, some not, I've so far been lucky. Next you could try reducing the 5V to the keyboard with a couple of silicone diodes in series (1N4001 or2 or3 ,almost anything) , each diode had approx 0.6V drop, so that would be about 3.8V to the keyboard, next try just one diode. This had been discussed before if you have a hunt around. Regards Kevin. Edited 2024-02-18 19:02 by Bleep |
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Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6787 |
The "CMM1.5" USB system works very nicely in my experience. In fact, PicoGAME won't have a PS2 socket. It will expect a USB keyboard, which can be plugged into the USB-A socket. You *can* use series resistors and a "safety" diode up to 3V3 to connect a 5V PS2 keyboard to a Pico instead of a proper level shifter - I've done it. I used 270R with BAT85 Schottky diodes for my original PicoMite VGA board. IIRC that resistor value was one used by HP or someone like that for connecting to a 3V3 FPGA. The diodes are important - don't use ordinary silicon types like 1N4148. I swapped to proper level shifters because it's probably safer in the long run. :) Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2135 |
As noted above many (perhaps most) PS/2 keyboards will work at 3.3V. I have only found one that wont. I have used 6.8kΩ pulldowns with the 5V keyboard and they reduced the voltage to 3.1V The data and clock pullups are usually current sources limited to less than 0.5mA so Schottky diodes from them to 3.3V also work. In fact ordinary diodes will do as the datasheet voltage limits are very conservative. Others have tested Din pins to 5.0V without failure. I have had pins going to Vsys (4.8V) without issue. |
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Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1611 |
I'm sorry but people are getting side-tracked by my ramblings. Leo wants to use a USB keyboard with a PicoMiteVGA. He doesn't want to buy a PS2 keyboard. Bill Keep safe. Live long and prosper. |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6787 |
You can probably simply power the keyboard from 5V but via a silicon diode. I doubt if any will complain about losing 0.6V. The maximum voltage on the pins can only be a current-limited 4V4 then, which (according to Raspberry Pi) the Pico will withstand. As I said, Bill - the "CMM1.5" usb system seems to work well. You do need a USB-TTL converter for the console & power connection though. Edited 2024-02-18 20:21 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Volhout Guru Joined: 05/03/2018 Location: NetherlandsPosts: 4233 |
Guys, Leo has a picomitVGA that has ps2 level shifters. Leo is looking for a way to use a non ps2 USB keyboard. I still think in his case the zero is a good solution, or the universal solution using a usb hub and a zero, or second pico. I tried that and it works fine. Search the forum for "hid2cdc" in the title. Volhout P.s. I bought my ps2 keyboard for 0.25 at a flee market, it needed just a clean. Edited 2024-02-18 22:04 by Volhout PicomiteVGA PETSCII ROBOTS |
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stanleyella Guru Joined: 25/06/2022 Location: United KingdomPosts: 2129 |
If the ps2 keyboard has the small ps2 plug and is black and looks modern, it's probably like mine and works at 3.3V or 5V. I cut the plug off and soldered molex pins. The picomite usb and picomiteVGAusb are fine using a usb to ttl converter, about the same price as a rpipico?  |
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LeoNicolas Guru Joined: 07/10/2020 Location: CanadaPosts: 479 |
As described by Turbo46 and Volhout, I'm trying to connect a modern mechanical USB keyboard to a PicoMite VGA with a PS2 connector. The direction is: USB KEYBOARD ==> PicoMite VGA PS2 Connector I don't have a PS2 Keyboard, and buying one is my last option.  Edited 2024-02-19 03:03 by LeoNicolas |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9115 |
You can always use the PicoMiteVGAUSB firmware. Power the Pico through VBUS Plug the keyboard into the Pico USB port via a USB-A female to micro-USB male adapter Then you are away If you also need a console then use a USB/UART on pins GP8 and GP9 |
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| LeoNicolas Guru Joined: 07/10/2020 Location: CanadaPosts: 479 |
Thank you Peter When you say "Power the Pico through VBUS", does it mean get 5v + gnd from a USB charger and connect it to the +5 and GND pins of the pico? Sorry for the noob question, I don't want to burn the board  |
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| matherp Guru Joined: 11/12/2012 Location: United KingdomPosts: 9115 |
I don't know Mick's board but you want to connect 5V to Pin 40 of the PicoMite or anything that routes to it |
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| Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1611 |
But it's certainly the easiest option. Just plug it in and go. No modes to the board, no soldering, no risk of damage and you don't have to swap keyboards back and forth. I would buy a mini keyboard such as this and be done with it. You will have to put up with a potentially inferior keyboard but it's a much simpler solution. Bill Keep safe. Live long and prosper. |
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| stanleyella Guru Joined: 25/06/2022 Location: United KingdomPosts: 2129 |
chipin in, usb kb works fine vga and lcd. usb to ttl powers picomite VSS pin next to usb.  |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6787 |
By default the incoming 5V supply feeds the Pico via a regulator onto the 3V3 rail and the switcher is disabled. I'm not sure if this is how Leo has built it? You can take the GND off 3V3EN and leave the regulator out. The barrel jack socket powers VSYS via a diode. There is no connection to VBUS, but it could simply be linked to VSYS to get 5V out of the USB. Isolating GP8 and GP9 might be a little awkward but you might be ok to just dab wires onto them for a USB-TTL converter. If that fails then the mosfets might have to be taken out or the traces to their source leads cut underneath the board. PS2 keyboards are still easy to find, luckily. :) Edited 2024-02-19 05:29 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| LeoNicolas Guru Joined: 07/10/2020 Location: CanadaPosts: 479 |
I found this page explaining different ways to power the pico board. https://projects.raspberrypi.org/en/projects/introduction-to-the-pico/12 |
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| stanleyella Guru Joined: 25/06/2022 Location: United KingdomPosts: 2129 |
I run picomite from linear 3.3v and 5v reg boards. 3.3v enable to ground. not really necessary in reality. The usb and power from usb to ttl adaptor is nice  |
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| LeoNicolas Guru Joined: 07/10/2020 Location: CanadaPosts: 479 |
stanleyella I will not have the USB connector available; I will connect the keyboard to it. I need to power the Pico from another place. I'm not sure exactly where and if I can connect a 5V line to the Pico without using the USB. |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6098 |
Leo, Disclaimer - I don't have a picomiteVGA and have not kept up with the various circuits. But. Connect both pin 40s together (and ground). That way power from your USB on the picomiteVGA comes out pin 40 and in pin 40 on the second module and that connects directly to the USB which will power the keyboard. Using pin 40 on both avoids any diodes getting in the way. The clock and data lines from the usb to ps2 converter pico connect to the pico pins on the picomiteVGA, not to the ps2 port. That way any level shifters on the picomiteVGA are avoided and you have 3.3V to 3.3V = happy camper. Clear as mud... Jim VK7JH MMedit MMBasic Help |
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| Mixtel90 Guru Joined: 05/10/2019 Location: United KingdomPosts: 6787 |
The USB version works like this: An incoming 5V comes from an external source - the console is a possible place. The PicoMite VGA Basic board also has a barel jack socket which is suitable. Only use a single source of supply though. The console is connected via a USB-TTL converter with the TTL side on GP8 and GP9 instead of the PS2 keyboard. These pins are configured as a serial port at 15.2kbd by default. The 5V rail can be taken from this converter. Normally there is a forward-biased diode from MBUS to VSYS on the Pico, to protect the USB connection from a supply on VSYS. In this case we don't want that diode as we are going to put 5V out, so you can power the Pico via MBUS or power via VSYS and link VSYS to MBUS to short the diode out. The Pico's USB is fed to a USB keyboard or a passive USB hub (not a powered one). You can't connect this USB to a PC now as there is a danger of damaging the USB port on the PC. You will need a USB-A female to micro USB male adapter to connect to the Pico's USB. The USB hub can accept keyboards, mice and some game controllers. I got a very cheap 4-port hub from ebay and it works fine. -------------------------- It's also possible to make an adapter (as shown earlier) that will accept a USB keyboard and convert the signals to PS2 to feed the PS2 input. This uses the standard software so USB mice and game controllers are not supported unless people write special software to do it. If using this method then the adapter Pico is simply powered from the same source as the main one. Edited 2024-02-19 07:49 by Mixtel90 Mick Zilog Inside! nascom.info for Nascom & Gemini Preliminary MMBasic docs & my PCB designs |
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| Turbo46 Guru Joined: 24/12/2017 Location: AustraliaPosts: 1611 |
Jim, I think Leo's preferred option now is to use the USB PicomiteVGA firmware so he can plug the USB keyboard into the Pico's USB socket. Leo, Can you please tell me which one of of Mick's many boards you have. I can't find it and I want to look at the circuit diagram. Bill Keep safe. Live long and prosper. |
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