Minerva Mk2 Remake

[techy]

= a bit off topic , but ;

Has anyone a copy of the schematic of the double-reset battery backup to the standard rtc of the ql ??

i can not find it anymore .................

[Martin_Head]

= a bit off topic , but ;

Has anyone a copy of the schematic of the double-reset battery backup to the standard rtc of the ql ??

i can not find it anymore .................

Is this the one you mean viewtopic.php?p=44693#p44693

[techy]

Yes !!


I consider making this as i need a pm 3 rom ql to have an rtc

[t0nyt]

Talking of batteries, does anyone have any thoughts on the battery to use with the Minerva Mk2 remake please?

Originally I was just going to use a CR2032, but I've just realised that the original had a rechargeable battery which suggests the board layout will be trying to re-charge the battery

My current thought is to use an ML2032

But I was wondering if anyone can offer any advise on this please?

Many thanks
Tony

[tofro]

Talking of batteries, does anyone have any thoughts on the battery to use with the Minerva Mk2 remake please?

Originally I was just going to use a CR2032, but I've just realised that the original had a rechargeable battery which suggests the board layout will be trying to re-charge the battery

My current thought is to use an ML2032

But I was wondering if anyone can offer any advise on this please?

Many thanks
Tony

Read the text file (in the _zip) next to the PDF you linked to - it is much more detailed and has all the info you need. Both on non-rechargeable batteries and what type you should chose. It also lists the mods you'll need to do to the QL PCB.

Note, depending on the board issue, you might also need to lift pin 40 of the 8302. Otherwise, the battery might try to run the whole QL.....

[t0nyt]

Talking of batteries, does anyone have any thoughts on the battery to use with the Minerva Mk2 remake please?

Originally I was just going to use a CR2032, but I've just realised that the original had a rechargeable battery which suggests the board layout will be trying to re-charge the battery

My current thought is to use an ML2032

But I was wondering if anyone can offer any advise on this please?

Many thanks
Tony

Read the text file (in the _zip) next to the PDF you linked to - it is much more detailed and has all the info you need. Both on non-rechargeable batteries and what type you should chose. It also lists the mods you'll need to do to the QL PCB.

Note, depending on the board issue, you might also need to lift pin 40 of the 8302. Otherwise, the battery might try to run the whole QL.....

Sorry Tofro, I don't have a clue how that document you link to relates to the Minerva Mk 2 board?

I also don't know what pdf I'm supposed to of linked to

Many thanks

[aalea]

Sorry for reply to late.

Regarding pins of the conector, I'm not sure because I use "standar" from Kicad, so probably it's reversed, I will check and update the PCB if need.

ML2032 is a litium rechargable battery and need a special charger circuit, you shall not conect to the minerva circuit, it's not safe.

CR2032 is a non recargable battery, i'm not sure if is safe to use it or not.

In any case, you can replace the R3 (edited, is not R2) with a second diode BAT42 and use any of CR/ML batteries, it will not charge, but is safe.

The original circuit use a 2x NiCd batteries (probably 1/3 AA size) in serie, this is a bit rare today, but you can replace with 2x AAA bateries in relative safe way, in any case the circuit charge is very basic.

[t0nyt]

Sorry for reply to late.

Regarding pins of the conector, I'm not sure because I use "standar" from Kicad, so probably it's reversed, I will check and update the PCB if need.

ML2032 is a litium rechargable battery and need a special charger circuit, you shall not conect to the minerva circuit, it's not safe.

CR2032 is a non recargable battery, i'm not sure if is safe to use it or not.

In any case, you can replace the R2 with a second diode BAT42 and use any of CR/ML batteries, it will not charge, but is safe.

The original circuit use a 2x NiCd batteries (probably 1/3 AA size) in serie, this is a bit rare today, but you can replace with 2x AAA bateries in relative safe way, in any case the circuit charge is very basic.

Many thanks for the reply aalea

I'm happy with disabling the recharge circuit, but as I'm not good at electronics would you be able to clarify what the orientation of the BAT42 (in place of R2) should be please?

I'll verify the the 12c pin layout with a multimeter once built

EDIT: reading the schematic I had assumed it was R3 that needed to be a diode to disable charging (or attach a diode between battery and +ve pin on 2 pin header), wish I understood how all this worked!

Many thanks
Tony

[aalea]

Yes, sorry key swap, is R3, (I edited the original message to avoid confusion in the future).
Check the picture attached, both diodes in the same position.

Charging circuit is very simple, a resistor limit the charging current, thats all:
* NiCd and NiMh batteries are expected to charge at a current about 1/10 of his capacity for arround 10-12h, this is the normal charge, and cut when voltage is not ingreasing any more. (about 1.4V/cell)
* NiCd and NiMh support trickle charging that is a small current to compensate the self-discharge, this is about 1/2400 of the current of the battery (1% a day), and it's suppous that with this current never overload the battery.
* When you overcharge the batteries, the excess of energy is transformed in heat, if the heat is high, can damage the internal chemistry of the battery and damage it.
* This is a non-acurrate description, but it's enought for our use.

When the QL is OFF, D1 avoid to power the QL from battery, so, only PCF8583 is powered, it need only 1V to hold the clock and consume about 0,01mA

When the QL is ON, on Katode of D1 there will be about 4,5V (Vcc-Vd1, 5V - 0,4V because is a schotky diode) and on the battery you will have between 2V and 2,8V depending on the charge of the battery, so a current will flow in direction to the battery of about (4-5-2)/120=20mA to (4.5-2.8)/120=14mA that will charge the battery at very low rate.

This current is so low rate, that even if you have a charged battery, the heat is disipated fast enought and not cause big impact in the life of the battery.

For a 1/3 AA 500mAh battery, as the current of the PCF + self-discharging is something about 0.25mAh, it last for about 3 month and it fully charge in 24h of QL use.

So not the best, but work, and lots of devices has similar charging circuits.

[t0nyt]

Yes, sorry key swap, is R3, (I edited the original message to avoid confusion in the future).
Check the picture attached, both diodes in the same position.

Charging circuit is very simple, a resistor limit the charging current, thats all:
* NiCd and NiMh batteries are expected to charge at a current about 1/10 of his capacity for arround 10-12h, this is the normal charge, and cut when voltage is not ingreasing any more. (about 1.4V/cell)
* NiCd and NiMh support trickle charging that is a small current to compensate the self-discharge, this is about 1/2400 of the current of the battery (1% a day), and it's suppous that with this current never overload the battery.
* When you overcharge the batteries, the excess of energy is transformed in heat, if the heat is high, can damage the internal chemistry of the battery and damage it.
* This is a non-acurrate description, but it's enought for our use.

When the QL is OFF, D1 avoid to power the QL from battery, so, only PCF8583 is powered, it need only 1V to hold the clock and consume about 0,01mA

When the QL is ON, on Katode of D1 there will be about 4,5V (Vcc-Vd1, 5V - 0,4V because is a schotky diode) and on the battery you will have between 2V and 2,8V depending on the charge of the battery, so a current will flow in direction to the battery of about (4-5-2)/120=20mA to (4.5-2.8)/120=14mA that will charge the battery at very low rate.

This current is so low rate, that even if you have a charged battery, the heat is disipated fast enought and not cause big impact in the life of the battery.

For a 1/3 AA 500mAh battery, as the current of the PCF + self-discharging is something about 0.25mAh, it last for about 3 month and it fully charge in 24h of QL use.

So not the best, but work, and lots of devices has similar charging circuits.

Many thanks aalea for the very comprehensive description

Many thanks
Tony