Build the 4.0 or Upgrade to 4.2.4


 
N

Neil Martin

New member
Way back in Oct. of 2013 I decided I was going to build the HM4.0, I ordered all the parts and was really excited to get to building; then we had a child and the wheels came off. Needless to say the parts have sat in the box for the past 14 months and haven't touched them. I think we are finally at a place where I can carve out enough time to get back to building, but clearly there have been some changes. It seems to me the most dramatic change is the option to use a thermocouple for the pit probe, it has also gotten a little more compact. Are there other changes that clearly make it worthwhile to go ahead and build the 4.2.4 over the 4.0? Having very little soldering experience I'm concerned about the surface soldering of the parts for the thermocouple so I would end up trying to find a PCB w/ those parts pre-soldered if that makes a big difference.
 
Personally, I'd go with the v4.2.4

You've got the majority of the parts already including some of the costlier items such as the voltage regulator and the LCD display. I just went through the mouser order list and after I removed all of the parts that you should have with the v4.0 it would be a $10 order + shipping, and that's still going to leave you with some spare resistors and capacitors.

Just order the bare heatermeter board with the SMD parts already on it for the TC and solder on the rest of the components.
 
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Hi Neil, I JUST built my first HM (4.2, the first cook is still going!) By the end of the process, I found the SMD parts relatively easy to get on the board, being only marginally more difficult the through-hole. This was due to understanding how to work with them, not vast improvements in soldering skills (which I had never done any of, SMD or otherwise, before this project). If you choose to do the 4.2 and solder the SMD components yourself, here are the pointers I would give.

1. Get some curly tweezers, you will need them.
2. When working with the SMD components, put a little solder on ONE pad first. Then place the SMD component in position, and reflow that pad. Then it is tacked down, and you can solder both sides more securely.
3. The TC amp is a real monster, because the pads are SOOO small. That said, if you just get a LITTLE solder on the iron, you can run it over the pads slowly and it will flow on. Then place the amp (notch/square/mark toward the close edge of the board, I screwed this up and had to pull it off and resolder) and run the iron over to reflow and tack it down. Then do the solder-on-iron trick on the other side. If you put too much down, solder wick is your friend.

Additional tips I wish I had known:
4. Clean any flux off your TC amp area. I had crazy readings until I did this (at the suggestion of Steve_M) and it did the trick.
5. Make sure you mount the LCD in the correct orientation! The screen goes on the OPPOSITE side of all the components (resistors, etc) I screwed this up and trashed the LCD, and if you look at the forums, a lot of other folks have done so as well.

I hope this is helpful.
 
Hmm, changes since HMv4.0....
Well, the 4.0 was a pretty good board, it had less noise on the probes than the 4.1, but....

The 4.0 was the last board that had the RCA jack for the blower output, from 4.1 and beyond the HM uses a CAT5 jack for the output. This CAT5 jack has the blower output and servo output wired to it by default, and you can use the 4 spare wires in the CAT5 wire for whatever you like, for instance, sending the probe output through the CAT5 jack as well. The 4.0 board does not have any header to connect a servo, however, you can connect a servo by jumpering a wire directly to a pin on the ATMEGA, +5v and gnd.

The HMv4.0 was the last board that pulsed the GND on the blower rather than the +12v, on the HMv.4.1 the blower drive circuit was changed to pulse the power instead (+12V), this way the servo and blower can now share a ground in the CAT5 cable. On HMv4.2 the blower drive circuit was updated again, this time to include a feedback circuit to the ATMega so the blower can run in the new VOLTAGE mode, rather than the standard pulse mode which creates more noise that can interfere with the probe readings.

Speaking of noise, in the HMv4.2 Bryan added an RC filter on each probe which GRATELY reduces the noise level on the probes. This not only makes the probes read more steadily, it makes the HM operate in a bit more relaxed fashion rather than hyper-correcting for noise spikes. Bryan actually re-routed the entire v4.2 board, for the first time keeping noisy power components away from temperature sensing component and paid attention to routing to keep sensor circuits isolated from power noise, these changes made the HMv4.2 the board with the least amount of noise picked up by the probes to date. On previous releases some probes had problems dropping off at room temps (though they work fine at grill temps), the clean running HMv4.2 will register probes down below freezing without an issue. This is nice if you do winter cooking, cause the HM will really flake out if the pit probe is dropping offline, which makes firing up the pit in the cold a PITA (I used to have to put the HM into manual blower mode until the pit heated up with older HM versions, that's all in the past with v4.2).

Finally, as you pointed out, the HMv4.2 mates with the rPi in a really low profile package, making the HMv4.2 fit into the smallest case yet for any HM. (least important difference if you ask me)

So, bottom line, I like the HMv4.0, it was a good board, the 4.1 was a bit rough (more noise), if you had a 4.1 I would say for sure you should update to 4.2... That said, I think the above improvements make moving from 4.0 to 4.2 worth it, the HMv4.2 is the best Heater Meter released to date.....

Keep in mind, parts wise the blower circuit is completely different, all the NPN transistors on the 4.0 have been changed to MOSFETS on the 4.2, so there are a lot of parts that are added/different on v4.2 compared to v4.0.....
 
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Here's a list of items you can safely remove from the mouser parts list as found on the HM v4.2 Hardware wiki page

571-1-2199298-9 - 28 DIP Socket
556-ATMEGA328P-PU - Atmega328P
595-SN74HC595N - Shift register for LCD and LEDs
810-PS1240P02BT - Audio Buzzer
580-OKI78SR51.5W36HC DC/DC Converter
649-68001-236HLF - Pin Header
72-T70YE-10K - 10K Trim pot
763-0216K1Z-FSA-GBW - LCD Display
688-SKQUAA - Multi-Directional Button < Not sold anymore, bonus for you!
653-B32-1610 - Plastic Button Cap
163-7620E-E - DC Power Connector

Just removing the the 3 items in red should drop the price by about $18-$20
 
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After you have removed items from the cart it's hard for us to tell if there is something you need that is missing...
Steve_M gave you a good list of the most costly items that are the same which you can eliminate, the rest of the stuff is so cheap... So I would just load up the HMv4.2 cart and pull out those components that have a significant cost and order that.... Keep in mind that the Thermocouple amp parts are in a second Mouser cart, so you need to order that cart too if you want to do the SMD TC stuff and have a Thermocouple Pit Probe.... Now that I mention it, I don't think Mouser has the TC jack, so you would have to order one of those from Newark or Omega as well...
 
Yep, sooner or later you're going to want to use a 10K resistor or a 0.1u cap for something else and you'll be glad you didn't bother removing what adds up to $2.50 in parts because it's going to cost you $8 in shipping to buy a $0.10 part :)
 
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