Casio CQ-1

 Casio CQ-1

A long time ago, I had a Casio CQ-1. 

It was a weird machine, I suppose, but it was a clock, and a stopwatch, and a calculator, which makes it pretty useful. And the calculator could tell you what day of the week any date was (well, in it's date range). It could calculate the number of days between two dates. And it was an alarm clock.

Not so long ago the batteries leaked and the CQ-1 was binned. This was a shame and I decided to get hold of another one, so bought one on ebay. This didn't turn out too well, as the device would only start up if I held my finger on one of the clock oscillator pins. I tried simulating a finger with various components, but the little chip seemed only happy with my finger. I never found out why, so I bought another CQ-1, hoping to either get enough bits to fix my original CQ-1 or get a unit I could fix. That didn't work out too well either, as it was utterly dead, and no amount of fingering could get it going again.  Aargh!. Third unit and this time all was well. It calculated dates and the stopwatch worked.

At least all was well until I came to use it after a day or two and the AA battery was flat. Aaargh! again. This CQ-1 has a strange fault where the supply that powers the VFD display seems to power up repeatedly even when the unit is off, and that eventually flattens the battery.

So, I decided to have a go at designing a replacement for the CQ-1 main PCB. This is the one that has the circuitry on it. This is a partially stripped PCB:

It attaches to a keyboard PCB which has one of the AA battery connections on it. The wire tabs connect to two 1.5V watch batteries that power the clock circuit. 

The first attempt at recreation is this:

There's a prototyping PCB (one of Mike Harrison's prototyping boards) with all the circuitry to create the voltages to run the ARM processor (3V3)and the higher voltage needed to run the VFD segments and digits (about 23V). The filament drive is conveniently 3V3 (ac). The PCB is attached to the front half of a CQ-1 which provides the switches and keys. All this circuitry runs off a single AA battery, or USB. As batteries are an evil that has to be tolerated, I did consider running this off just USB, but decided that it was too limiting. i didn't want to use the original CQ-1 PSU as I've never seen one, and USB is just so convenient. I haven't carried over the silver oxide batteries that run the clock, instead the RTC chip runs directly off the battery. It is a low power chip so that's not a problem. If there's 3V3 then it runs off that too, so you can plug a USB cable in when changing the AA battery.

This is a close up of the prototype PCB.

There's a blue pill providing an ARM processor, programmed with an ST-LINK. There's two dc-dc converters, one to go from 1V5 to 3V3 and one to go from 3V3 to 23V (-ish). The 23V supply is switchable from the processor and turns the display on and off. The VFD is driven from a MAX6921 chip which has a serial connection to the processor. The timekeeping is provided by an MCP7940 chip with it's own crystal. This is attached over I2C to the processor. i took a VFD tube from a donor CQ-1 and that is used as the display. The beeper is also from a CQ-1. Due to the STM32F103C8 on the blue pill not having enough GPIOs to handle all this hardware and scan the keypad, a GPIO expander is used on this PCB to provide more GPIOs. This is accessed using I2C.

Of course, this doesn't fit in the original case, so a V2.0 PCB has been created that does:

This is basically the same circuit, but the dc-dc converters are now in component form on the PCB, and the GPIO expander has been dropped as a larger STM32 chip with more GPIOs has been used. This is capable of all the IO and keypad scanning. It also has more flash and RAM (512K of flash and 64K of RAM). As the STM32F103 chips are all very compatible there are a few options for flash and RAM simply by fitting a different variant of the chip.

I've also added the connections for an OLED display on this PCB so if the CQ-1 VFD is broken then you can use a dot matrix OLED display. The 23V dc-dc converter can be left out if the OLED is used, as well.

Here's the first populated PCB in a case:

It fits nicely, the wires coming out are the ST-LINK programmer wires. The USB power goes in through the battery cover latch hole which I filed out so the USB socket was accessible. The circuit should run off a single AA battery as well (the prototype did, but I've not tested the new PCB yet). I'll need to print a connector for the positive terminal of the battery, the negative is a spring on the keypad PCB.

Here's the front side of the PCB:

Again the beeper and VFD tube are from a CQ-1. The keypad PCB is mounted using 0.1" plug and socket connectors, the spacing was perfect, even though the original CQ-1 uses copper strips held together with plastic.

The PCB needs a modification as I got one signal wrong, the keypad connector is out by 0.1" for five connections, the 23V dc-dc converter inductor whistles, and the mounting hole for the beeper is too small, but other than that I'm very happy with it. It fits the case well.

There's a few things left to do. The display is a bit dim, which is probably the 23V dc-dc converter needing to be 26V or so. There's a lot of code to write if this is going to be the same as a CQ-1 but there's a rudimentary stopwatch and integer-only calculator, together with a clock you can't set, but writing the code is the fun bit...

See it working here:

Some pictures of it operating:

The USB cable that is powering it and the programming wires that come off a header on the PCB:

And displaying some characters that the original just can't manage: