Following on with step 1a from the Mad Scientist Hut article: Making a high resolution ADC from an Arduino Mini Pro

In order to make a high resolution DC source we need a 16 bit PWM output from the Arduino. The standard libraries give you access to 8bits on the PWM pins, this only gives 256 discrete levels, if you had 16bits it will yield 65535 steps. Timer1 on the Mini Pro and UNO is capable of going into 16bit mode. With just a little Googling I found a library that give access to the 16bit timer modes, as well as letting you reprogram the PWM output frequency, the library was created by the user ‘runnerup’  AKA Sam Knight (as the copyright header in the lib indicates) in the Arduino forums: Here

The library is located here: PWM Frequency Library , the library also is supposed to work on both  the Arduino Mega and UNO.

Timer1 is the only 16bit timer on the atmega328 (UNO and Mini Pro) and it only comes out on two pins, 9 and 10. If you were to use the Mega  it has many more pins capable of 16 bit mode on the PWM outputs. I got the below timer/bit/pins table from: Advanced Arduino: direct use of ATmega counter/timers

timer	bits	channel	Arduino pin	Mega pin
timer0	8	A	6	13
timer0	8	B	5	4
timer1	16	A	9	11
timer1	16	B	10	12
timer2	8	A	11	10
timer2	8	B	3	9
timer3	16	A	–	5
timer3	16	B	–	2
timer3	16	C	–	3
timer4	16	A	–	6
timer4	16	B	–	7
timer4	16	C	–	8
timer5	16	A	–	44
timer5	16	B	–	45
timer5	16	C	–	46

Being able to reprogram the frequency is very important since it has an effect on the actual resolution that can be achieved.  See the table at the bottom for an output from the demo program from the PWM Frequency library that shows the differences for frequency to resolution. Since 131 Hz gives almost 16 bits of resolution at 61069 steps, this is what frequency I am going to use as I experiment. This will give approximately 81uV DC filtered step sizes on average using a 5V Mini Pro, we will try to verify this later, the best meter I have here is good for 100uV resolution in the 11V range, I will try to borrow one that has higher resolution in the next couple of weeks.

So lets try it out…

I wrote a quick program to try a few things: first did the frequency set?  second does high resolution PWM work on both channels 9 and 10 independently ( there was a note in the library that you would lose the second channel )?  third is it really high resolution?

We set PWM on channel 9 and 10 separately at a frequency of 131HZ  ( reciprocal of 131Hz is 0.0076335…. seconds) the period should be about 7.63mS. See screen shot, yes to both of those!

Now does the 16 bit resolution work. The reciprocal of 131Hz divided by 61069 steps is ~125nS.  This picture shows where I set the PWM to a setting of 1. Yes it works!

Here it is with PWM set to 2 and yes it is now ~250nS

Now onto designing a filter to get DC out of this….

Demonstrate Frequency Effect On Resolution Table ( I only ran it to 3931 HZ, but you get the idea….)

1	Hz	7813	steps	12	bits
11	Hz	2841	steps	11	bits
21	Hz	5953	steps	12	bits
31	Hz	4033	steps	11	bits
41	Hz	3049	steps	11	bits
51	Hz	2451	steps	11	bits
61	Hz	2050	steps	11	bits
71	Hz	14085	steps	13	bits
81	Hz	12346	steps	13	bits
91	Hz	10990	steps	13	bits
101	Hz	9901	steps	13	bits
111	Hz	9010	steps	13	bits
121	Hz	8265	steps	13	bits
131	Hz	61069	steps	15	bits
141	Hz	56738	steps	15	bits
151	Hz	52981	steps	15	bits
161	Hz	49690	steps	15	bits
171	Hz	46784	steps	15	bits
181	Hz	44199	steps	15	bits
191	Hz	41885	steps	15	bits
201	Hz	39801	steps	15	bits
211	Hz	37915	steps	15	bits
221	Hz	36200	steps	15	bits
231	Hz	34633	steps	15	bits
241	Hz	33196	steps	15	bits
251	Hz	31873	steps	14	bits
261	Hz	30652	steps	14	bits
271	Hz	29521	steps	14	bits
281	Hz	28470	steps	14	bits
291	Hz	27492	steps	14	bits
301	Hz	26579	steps	14	bits
311	Hz	25724	steps	14	bits
321	Hz	24923	steps	14	bits
331	Hz	24170	steps	14	bits
341	Hz	23461	steps	14	bits
351	Hz	22793	steps	14	bits
361	Hz	22161	steps	14	bits
371	Hz	21564	steps	14	bits
381	Hz	20998	steps	14	bits
391	Hz	20461	steps	14	bits
401	Hz	19951	steps	14	bits
411	Hz	19465	steps	14	bits
421	Hz	19003	steps	14	bits
431	Hz	18562	steps	14	bits
441	Hz	18141	steps	14	bits
451	Hz	17739	steps	14	bits
461	Hz	17354	steps	14	bits
471	Hz	16986	steps	14	bits
481	Hz	16633	steps	14	bits
491	Hz	16294	steps	13	bits
501	Hz	15969	steps	13	bits
511	Hz	15656	steps	13	bits
521	Hz	15356	steps	13	bits
531	Hz	15066	steps	13	bits
541	Hz	14788	steps	13	bits
551	Hz	14520	steps	13	bits
561	Hz	14261	steps	13	bits
571	Hz	14011	steps	13	bits
581	Hz	13770	steps	13	bits
591	Hz	13537	steps	13	bits
601	Hz	13312	steps	13	bits
611	Hz	13094	steps	13	bits
621	Hz	12883	steps	13	bits
631	Hz	12679	steps	13	bits
641	Hz	12481	steps	13	bits
651	Hz	12289	steps	13	bits
661	Hz	12103	steps	13	bits
671	Hz	11923	steps	13	bits
681	Hz	11748	steps	13	bits
691	Hz	11578	steps	13	bits
701	Hz	11413	steps	13	bits
711	Hz	11252	steps	13	bits
721	Hz	11096	steps	13	bits
731	Hz	10944	steps	13	bits
741	Hz	10797	steps	13	bits
751	Hz	10653	steps	13	bits
761	Hz	10513	steps	13	bits
771	Hz	10377	steps	13	bits
781	Hz	10244	steps	13	bits
791	Hz	10114	steps	13	bits
801	Hz	9988	steps	13	bits
811	Hz	9865	steps	13	bits
821	Hz	9745	steps	13	bits
831	Hz	9627	steps	13	bits
841	Hz	9513	steps	13	bits
851	Hz	9401	steps	13	bits
861	Hz	9292	steps	13	bits
871	Hz	9185	steps	13	bits
881	Hz	9081	steps	13	bits
891	Hz	8979	steps	13	bits
901	Hz	8880	steps	13	bits
911	Hz	8782	steps	13	bits
921	Hz	8687	steps	13	bits
931	Hz	8593	steps	13	bits
941	Hz	8502	steps	13	bits
951	Hz	8413	steps	13	bits
961	Hz	8325	steps	13	bits
971	Hz	8239	steps	13	bits
981	Hz	8155	steps	12	bits
991	Hz	8073	steps	12	bits
1001	Hz	7993	steps	12	bits
1011	Hz	7913	steps	12	bits
1021	Hz	7836	steps	12	bits
1031	Hz	7760	steps	12	bits
1041	Hz	7685	steps	12	bits
1051	Hz	7612	steps	12	bits
1061	Hz	7541	steps	12	bits
1071	Hz	7470	steps	12	bits
1081	Hz	7401	steps	12	bits
1091	Hz	7333	steps	12	bits
1101	Hz	7267	steps	12	bits
1111	Hz	7201	steps	12	bits
1121	Hz	7137	steps	12	bits
1131	Hz	7074	steps	12	bits
1141	Hz	7012	steps	12	bits
1151	Hz	6951	steps	12	bits
1161	Hz	6891	steps	12	bits
1171	Hz	6832	steps	12	bits
1181	Hz	6774	steps	12	bits
1191	Hz	6718	steps	12	bits
1201	Hz	6662	steps	12	bits
1211	Hz	6607	steps	12	bits
1221	Hz	6553	steps	12	bits
1231	Hz	6499	steps	12	bits
1241	Hz	6447	steps	12	bits
1251	Hz	6395	steps	12	bits
1261	Hz	6345	steps	12	bits
1271	Hz	6295	steps	12	bits
1281	Hz	6246	steps	12	bits
1291	Hz	6197	steps	12	bits
1301	Hz	6150	steps	12	bits
1311	Hz	6103	steps	12	bits
1321	Hz	6057	steps	12	bits
1331	Hz	6011	steps	12	bits
1341	Hz	5966	steps	12	bits
1351	Hz	5922	steps	12	bits
1361	Hz	5879	steps	12	bits
1371	Hz	5836	steps	12	bits
1381	Hz	5793	steps	12	bits
1391	Hz	5752	steps	12	bits
1401	Hz	5711	steps	12	bits
1411	Hz	5670	steps	12	bits
1421	Hz	5630	steps	12	bits
1431	Hz	5591	steps	12	bits
1441	Hz	5552	steps	12	bits
1451	Hz	5514	steps	12	bits
1461	Hz	5476	steps	12	bits
1471	Hz	5439	steps	12	bits
1481	Hz	5402	steps	12	bits
1491	Hz	5366	steps	12	bits
1501	Hz	5330	steps	12	bits
1511	Hz	5295	steps	12	bits
1521	Hz	5260	steps	12	bits
1531	Hz	5226	steps	12	bits
1541	Hz	5192	steps	12	bits
1551	Hz	5158	steps	12	bits
1561	Hz	5125	steps	12	bits
1571	Hz	5093	steps	12	bits
1581	Hz	5061	steps	12	bits
1591	Hz	5029	steps	12	bits
1601	Hz	4997	steps	12	bits
1611	Hz	4966	steps	12	bits
1621	Hz	4936	steps	12	bits
1631	Hz	4905	steps	12	bits
1641	Hz	4876	steps	12	bits
1651	Hz	4846	steps	12	bits
1661	Hz	4817	steps	12	bits
1671	Hz	4788	steps	12	bits
1681	Hz	4760	steps	12	bits
1691	Hz	4731	steps	12	bits
1701	Hz	4704	steps	12	bits
1711	Hz	4676	steps	12	bits
1721	Hz	4649	steps	12	bits
1731	Hz	4622	steps	12	bits
1741	Hz	4596	steps	12	bits
1751	Hz	4569	steps	12	bits
1761	Hz	4543	steps	12	bits
1771	Hz	4518	steps	12	bits
1781	Hz	4492	steps	12	bits
1791	Hz	4467	steps	12	bits
1801	Hz	4442	steps	12	bits
1811	Hz	4418	steps	12	bits
1821	Hz	4394	steps	12	bits
1831	Hz	4370	steps	12	bits
1841	Hz	4346	steps	12	bits
1851	Hz	4322	steps	12	bits
1861	Hz	4299	steps	12	bits
1871	Hz	4276	steps	12	bits
1881	Hz	4254	steps	12	bits
1891	Hz	4231	steps	12	bits
1901	Hz	4209	steps	12	bits
1911	Hz	4187	steps	12	bits
1921	Hz	4165	steps	12	bits
1931	Hz	4143	steps	12	bits
1941	Hz	4122	steps	12	bits
1951	Hz	4101	steps	12	bits
1961	Hz	4080	steps	11	bits
1971	Hz	4059	steps	11	bits
1981	Hz	4039	steps	11	bits
1991	Hz	4019	steps	11	bits
2001	Hz	3999	steps	11	bits
2011	Hz	3979	steps	11	bits
2021	Hz	3959	steps	11	bits
2031	Hz	3939	steps	11	bits
2041	Hz	3920	steps	11	bits
2051	Hz	3901	steps	11	bits
2061	Hz	3882	steps	11	bits
2071	Hz	3863	steps	11	bits
2081	Hz	3845	steps	11	bits
2091	Hz	3826	steps	11	bits
2101	Hz	3808	steps	11	bits
2111	Hz	3790	steps	11	bits
2121	Hz	3772	steps	11	bits
2131	Hz	3755	steps	11	bits
2141	Hz	3737	steps	11	bits
2151	Hz	3720	steps	11	bits
2161	Hz	3702	steps	11	bits
2171	Hz	3685	steps	11	bits
2181	Hz	3669	steps	11	bits
2191	Hz	3652	steps	11	bits
2201	Hz	3635	steps	11	bits
2211	Hz	3619	steps	11	bits
2221	Hz	3602	steps	11	bits
2231	Hz	3586	steps	11	bits
2241	Hz	3570	steps	11	bits
2251	Hz	3554	steps	11	bits
2261	Hz	3539	steps	11	bits
2271	Hz	3523	steps	11	bits
2281	Hz	3508	steps	11	bits
2291	Hz	3492	steps	11	bits
2301	Hz	3477	steps	11	bits
2311	Hz	3462	steps	11	bits
2321	Hz	3447	steps	11	bits
2331	Hz	3433	steps	11	bits
2341	Hz	3418	steps	11	bits
2351	Hz	3403	steps	11	bits
2361	Hz	3389	steps	11	bits
2371	Hz	3375	steps	11	bits
2381	Hz	3360	steps	11	bits
2391	Hz	3346	steps	11	bits
2401	Hz	3332	steps	11	bits
2411	Hz	3319	steps	11	bits
2421	Hz	3305	steps	11	bits
2431	Hz	3291	steps	11	bits
2441	Hz	3278	steps	11	bits
2451	Hz	3264	steps	11	bits
2461	Hz	3251	steps	11	bits
2471	Hz	3238	steps	11	bits
2481	Hz	3225	steps	11	bits
2491	Hz	3212	steps	11	bits
2501	Hz	3199	steps	11	bits
2511	Hz	3186	steps	11	bits
2521	Hz	3174	steps	11	bits
2531	Hz	3161	steps	11	bits
2541	Hz	3149	steps	11	bits
2551	Hz	3137	steps	11	bits
2561	Hz	3124	steps	11	bits
2571	Hz	3112	steps	11	bits
2581	Hz	3100	steps	11	bits
2591	Hz	3088	steps	11	bits
2601	Hz	3076	steps	11	bits
2611	Hz	3064	steps	11	bits
2621	Hz	3053	steps	11	bits
2631	Hz	3041	steps	11	bits
2641	Hz	3030	steps	11	bits
2651	Hz	3018	steps	11	bits
2661	Hz	3007	steps	11	bits
2671	Hz	2996	steps	11	bits
2681	Hz	2984	steps	11	bits
2691	Hz	2973	steps	11	bits
2701	Hz	2962	steps	11	bits
2711	Hz	2951	steps	11	bits
2721	Hz	2941	steps	11	bits
2731	Hz	2930	steps	11	bits
2741	Hz	2919	steps	11	bits
2751	Hz	2909	steps	11	bits
2761	Hz	2898	steps	11	bits
2771	Hz	2888	steps	11	bits
2781	Hz	2877	steps	11	bits
2791	Hz	2867	steps	11	bits
2801	Hz	2857	steps	11	bits
2811	Hz	2846	steps	11	bits
2821	Hz	2836	steps	11	bits
2831	Hz	2826	steps	11	bits
2841	Hz	2816	steps	11	bits
2851	Hz	2807	steps	11	bits
2861	Hz	2797	steps	11	bits
2871	Hz	2787	steps	11	bits
2881	Hz	2777	steps	11	bits
2891	Hz	2768	steps	11	bits
2901	Hz	2758	steps	11	bits
2911	Hz	2749	steps	11	bits
2921	Hz	2739	steps	11	bits
2931	Hz	2730	steps	11	bits
2941	Hz	2721	steps	11	bits
2952	Hz	2711	steps	11	bits
2961	Hz	2702	steps	11	bits
2971	Hz	2693	steps	11	bits
2981	Hz	2684	steps	11	bits
2991	Hz	2675	steps	11	bits
3001	Hz	2666	steps	11	bits
3012	Hz	2657	steps	11	bits
3021	Hz	2649	steps	11	bits
3031	Hz	2640	steps	11	bits
3041	Hz	2631	steps	11	bits
3051	Hz	2623	steps	11	bits
3061	Hz	2614	steps	11	bits
3071	Hz	2606	steps	11	bits
3081	Hz	2597	steps	11	bits
3091	Hz	2589	steps	11	bits
3101	Hz	2580	steps	11	bits
3111	Hz	2572	steps	11	bits
3121	Hz	2564	steps	11	bits
3131	Hz	2556	steps	11	bits
3142	Hz	2547	steps	11	bits
3152	Hz	2539	steps	11	bits
3162	Hz	2531	steps	11	bits
3172	Hz	2523	steps	11	bits
3182	Hz	2515	steps	11	bits
3191	Hz	2508	steps	11	bits
3201	Hz	2500	steps	11	bits
3211	Hz	2492	steps	11	bits
3221	Hz	2484	steps	11	bits
3231	Hz	2477	steps	11	bits
3241	Hz	2469	steps	11	bits
3252	Hz	2461	steps	11	bits
3261	Hz	2454	steps	11	bits
3271	Hz	2446	steps	11	bits
3281	Hz	2439	steps	11	bits
3292	Hz	2431	steps	11	bits
3301	Hz	2424	steps	11	bits
3311	Hz	2417	steps	11	bits
3322	Hz	2409	steps	11	bits
3331	Hz	2402	steps	11	bits
3341	Hz	2395	steps	11	bits
3351	Hz	2388	steps	11	bits
3361	Hz	2381	steps	11	bits
3371	Hz	2374	steps	11	bits
3381	Hz	2367	steps	11	bits
3391	Hz	2360	steps	11	bits
3401	Hz	2353	steps	11	bits
3411	Hz	2346	steps	11	bits
3421	Hz	2339	steps	11	bits
3432	Hz	2332	steps	11	bits
3442	Hz	2325	steps	11	bits
3451	Hz	2319	steps	11	bits
3461	Hz	2312	steps	11	bits
3472	Hz	2305	steps	11	bits
3481	Hz	2299	steps	11	bits
3491	Hz	2292	steps	11	bits
3501	Hz	2286	steps	11	bits
3511	Hz	2279	steps	11	bits
3521	Hz	2273	steps	11	bits
3532	Hz	2266	steps	11	bits
3541	Hz	2260	steps	11	bits
3552	Hz	2253	steps	11	bits
3561	Hz	2247	steps	11	bits
3571	Hz	2241	steps	11	bits
3581	Hz	2235	steps	11	bits
3592	Hz	2228	steps	11	bits
3601	Hz	2222	steps	11	bits
3611	Hz	2216	steps	11	bits
3621	Hz	2210	steps	11	bits
3631	Hz	2204	steps	11	bits
3641	Hz	2198	steps	11	bits
3651	Hz	2192	steps	11	bits
3661	Hz	2186	steps	11	bits
3671	Hz	2180	steps	11	bits
3681	Hz	2174	steps	11	bits
3691	Hz	2168	steps	11	bits
3701	Hz	2162	steps	11	bits
3712	Hz	2156	steps	11	bits
3722	Hz	2150	steps	11	bits
3731	Hz	2145	steps	11	bits
3741	Hz	2139	steps	11	bits
3752	Hz	2133	steps	11	bits
3761	Hz	2128	steps	11	bits
3771	Hz	2122	steps	11	bits
3782	Hz	2116	steps	11	bits
3791	Hz	2111	steps	11	bits
3802	Hz	2105	steps	11	bits
3811	Hz	2100	steps	11	bits
3822	Hz	2094	steps	11	bits
3831	Hz	2089	steps	11	bits
3842	Hz	2083	steps	11	bits
3851	Hz	2078	steps	11	bits
3861	Hz	2073	steps	11	bits
3872	Hz	2067	steps	11	bits
3881	Hz	2062	steps	11	bits
3891	Hz	2057	steps	11	bits
3902	Hz	2051	steps	11	bits
3911	Hz	2046	steps	10	bits
3921	Hz	2041	steps	10	bits
3931	Hz	2036	steps	10	bits